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https://github.com/tobast/libunwind-eh_elf.git
synced 2024-11-22 15:47:37 +01:00
Reduce stack use and apply CONFIG_DEBUG_FRAME to more code.
Currently, libunwind allocates several PATH_MAX entries on stack, while trying to find a binary via /proc/.../maps. However stack space may be at premium (especially when sigaltstack is used), and PATH_MAX on Linux is 4096, while SIGSTKSZ is only 8192 on x86. Attached patch eliminates multiple PATH_MAX stack allocations, and simplifies code in maps_next, at the cost of being unable to do anything if we can't mmap one page. It appears to me that under such low-memory conditions, libunwind will fail shortly elsewhere anyway. This patch also disables more of debug_frame-handling code when CONFIG_DEBUG_FRAME is undefined. Tested on Linux/x86_64 with and without CONFIG_DEBUG_FRAME, no regressions.
This commit is contained in:
Paul Pluzhnikov
Arun Sharma
parent
fc2934aade
commit
b56375e76a
4 changed files with 82 additions and 106 deletions
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@ -221,14 +221,6 @@ load_debug_frame (const char *file, char **buf, size_t *bufsize, int is_local)
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return 0;
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}
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#else
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static int
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load_debug_frame (const char *file, char **buf, size_t *bufsize, int is_local)
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{
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return 1;
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}
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#endif /* CONFIG_DEBUG_FRAME */
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/* Locate the binary which originated the contents of address ADDR. Return
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the name of the binary in *name (space is allocated by the caller)
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@ -244,10 +236,16 @@ find_binary_for_address (unw_word_t ip, char *name, size_t name_size)
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unsigned long segbase, mapoff, hi;
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maps_init (&mi, pid);
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while (maps_next (&mi, &segbase, &hi, &mapoff, name, name_size))
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while (maps_next (&mi, &segbase, &hi, &mapoff))
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if (ip >= segbase && ip < hi)
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{
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found = 1;
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size_t len = strlen (mi.path);
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if (len + 1 <= name_size)
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{
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memcpy (name, mi.path, len + 1);
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found = 1;
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}
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break;
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}
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maps_close (&mi);
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@ -400,6 +398,8 @@ debug_frame_tab_compare (const void *a, const void *b)
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return 0;
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}
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#endif /* CONFIG_DEBUG_FRAME */
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/* ptr is a pointer to a callback_data structure and, on entry,
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member ip contains the instruction-pointer we're looking
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for. */
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@ -575,6 +575,8 @@ callback (struct dl_phdr_info *info, size_t size, void *ptr)
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}
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}
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#ifdef CONFIG_DEBUG_FRAME
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Debug (15, "Trying to find .debug_frame\n");
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di = &cb_data->di_debug;
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fdesc = locate_debug_info (unw_local_addr_space, info, ip, info->dlpi_name);
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@ -707,6 +709,7 @@ callback (struct dl_phdr_info *info, size_t size, void *ptr)
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(long) di->u.ti.segbase, (long) di->u.ti.table_len,
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(long) di->gp, (long) di->u.ti.table_data);
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}
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#endif /* CONFIG_DEBUG_FRAME */
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return found;
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}
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@ -36,23 +36,28 @@ tdep_get_elf_image (struct elf_image *ei, pid_t pid, unw_word_t ip,
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unsigned long *segbase, unsigned long *mapoff)
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{
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struct map_iterator mi;
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char path[PATH_MAX];
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int found = 0;
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int found = 0, rc;
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unsigned long hi;
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maps_init (&mi, pid);
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while (maps_next (&mi, segbase, &hi, mapoff, path, sizeof (path)))
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if (maps_init (&mi, pid) < 0)
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return -1;
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while (maps_next (&mi, segbase, &hi, mapoff))
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if (ip >= *segbase && ip < hi)
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{
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found = 1;
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break;
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}
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maps_close (&mi);
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if (!found)
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return -1;
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{
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maps_close (&mi);
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return -1;
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}
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return elf_map_image (ei, path);
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rc = elf_map_image (ei, mi.path);
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maps_close (&mi);
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return rc;
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}
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#endif /* UNW_REMOTE_ONLY */
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136
src/os-linux.h
136
src/os-linux.h
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@ -34,6 +34,7 @@ struct map_iterator
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size_t buf_size;
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char *buf;
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char *buf_end;
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char *path;
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};
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static inline char *
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@ -61,33 +62,33 @@ ltoa (char *buf, long val)
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return buf + len;
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}
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static inline void
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static inline int
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maps_init (struct map_iterator *mi, pid_t pid)
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{
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char path[PATH_MAX], *cp;
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char path[sizeof ("/proc/0123456789/maps")], *cp;
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memcpy (path, "/proc/", 6);
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cp = ltoa (path + 6, pid);
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assert (cp + 6 < path + sizeof (path));
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memcpy (cp, "/maps", 6);
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mi->fd = open (path, O_RDONLY);
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mi->offset = 0;
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mi->buf_size = 0;
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cp = NULL;
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if (mi->fd >= 0)
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{
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/* Try to allocate a page-sized buffer. If that fails, we'll
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fall back on reading one line at a time. */
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/* Try to allocate a page-sized buffer. */
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mi->buf_size = getpagesize ();
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cp = mmap (0, mi->buf_size, PROT_READ | PROT_WRITE,
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MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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if (cp == MAP_FAILED)
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cp = NULL;
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return -1;
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else
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cp += mi->buf_size;
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{
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mi->offset = 0;
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mi->buf = mi->buf_end = cp + mi->buf_size;
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return 0;
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}
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}
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mi->buf = mi->buf_end = cp;
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return -1;
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}
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static inline char *
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@ -184,7 +185,7 @@ scan_string (char *cp, char *valp, size_t buf_size)
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while (*cp != ' ' && *cp != '\t' && *cp != '\0')
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{
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if (i < buf_size - 1)
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if ((valp != NULL) && (i < buf_size - 1))
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valp[i++] = *cp;
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++cp;
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}
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@ -196,12 +197,10 @@ scan_string (char *cp, char *valp, size_t buf_size)
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static inline int
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maps_next (struct map_iterator *mi,
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unsigned long *low, unsigned long *high, unsigned long *offset,
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char *path, size_t path_size)
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unsigned long *low, unsigned long *high, unsigned long *offset)
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{
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char line[256 + PATH_MAX], perm[16], dash, colon, *cp;
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char perm[16], dash, colon, *cp;
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unsigned long major, minor, inum;
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size_t to_read = 256; /* most lines fit in 256 characters easy */
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ssize_t i, nread;
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if (mi->fd < 0)
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@ -209,80 +208,52 @@ maps_next (struct map_iterator *mi,
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while (1)
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{
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if (mi->buf)
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ssize_t bytes_left = mi->buf_end - mi->buf;
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char *eol = NULL;
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for (i = 0; i < bytes_left; ++i)
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{
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ssize_t bytes_left = mi->buf_end - mi->buf;
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char *eol = NULL;
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for (i = 0; i < bytes_left; ++i)
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if (mi->buf[i] == '\n')
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{
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if (mi->buf[i] == '\n')
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{
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eol = mi->buf + i;
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break;
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}
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else if (mi->buf[i] == '\0')
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break;
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eol = mi->buf + i;
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break;
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}
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if (!eol)
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{
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/* copy down the remaining bytes, if any */
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if (bytes_left > 0)
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memmove (mi->buf_end - mi->buf_size, mi->buf, bytes_left);
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mi->buf = mi->buf_end - mi->buf_size;
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nread = read (mi->fd, mi->buf + bytes_left,
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mi->buf_size - bytes_left);
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if (nread <= 0)
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return 0;
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else if ((size_t) (nread + bytes_left) < mi->buf_size)
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{
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/* Move contents to the end of the buffer so we
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maintain the invariant that all bytes between
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mi->buf and mi->buf_end are valid. */
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memmove (mi->buf_end - nread - bytes_left, mi->buf,
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nread + bytes_left);
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mi->buf = mi->buf_end - nread - bytes_left;
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}
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eol = mi->buf + bytes_left + nread - 1;
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for (i = bytes_left; i < bytes_left + nread; ++i)
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if (mi->buf[i] == '\n')
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{
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eol = mi->buf + i;
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break;
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}
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}
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cp = mi->buf;
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mi->buf = eol + 1;
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*eol = '\0';
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else if (mi->buf[i] == '\0')
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break;
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}
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else
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if (!eol)
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{
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/* maps_init() wasn't able to allocate a buffer; do it the
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slow way. */
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lseek (mi->fd, mi->offset, SEEK_SET);
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/* copy down the remaining bytes, if any */
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if (bytes_left > 0)
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memmove (mi->buf_end - mi->buf_size, mi->buf, bytes_left);
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if ((nread = read (mi->fd, line, to_read)) <= 0)
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mi->buf = mi->buf_end - mi->buf_size;
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nread = read (mi->fd, mi->buf + bytes_left,
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mi->buf_size - bytes_left);
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if (nread <= 0)
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return 0;
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for (i = 0; i < nread && line[i] != '\n'; ++i)
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/* skip */;
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if (i < nread)
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else if ((size_t) (nread + bytes_left) < mi->buf_size)
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{
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line[i] = '\0';
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mi->offset += i + 1;
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/* Move contents to the end of the buffer so we
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maintain the invariant that all bytes between
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mi->buf and mi->buf_end are valid. */
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memmove (mi->buf_end - nread - bytes_left, mi->buf,
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nread + bytes_left);
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mi->buf = mi->buf_end - nread - bytes_left;
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}
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else
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{
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if (to_read < sizeof (line))
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to_read = sizeof (line) - 1;
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else
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mi->offset += nread; /* not supposed to happen... */
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continue; /* duh, no newline found */
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}
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cp = line;
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eol = mi->buf + bytes_left + nread - 1;
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for (i = bytes_left; i < bytes_left + nread; ++i)
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if (mi->buf[i] == '\n')
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{
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eol = mi->buf + i;
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break;
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}
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}
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cp = mi->buf;
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mi->buf = eol + 1;
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*eol = '\0';
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/* scan: "LOW-HIGH PERM OFFSET MAJOR:MINOR INUM PATH" */
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cp = scan_hex (cp, low);
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@ -294,7 +265,10 @@ maps_next (struct map_iterator *mi,
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cp = scan_char (cp, &colon);
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cp = scan_hex (cp, &minor);
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cp = scan_dec (cp, &inum);
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cp = scan_string (cp, path, path_size);
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cp = mi->path = skip_whitespace (cp);
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if (!cp)
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continue;
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cp = scan_string (cp, NULL, 0);
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if (!cp || dash != '-' || colon != ':')
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continue; /* skip line with unknown or bad format */
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return 1;
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@ -38,12 +38,6 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
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#include <unistd.h>
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#include <libunwind.h>
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#if UNW_TARGET_X86 || UNW_TARGET_X86_64 || UNW_TARGET_ARM
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# define STACK_SIZE (128*1024) /* On x86/-64 and ARM, SIGSTKSZ is too small */
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#else
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# define STACK_SIZE SIGSTKSZ
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#endif
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#define panic(args...) \
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{ fprintf (stderr, args); exit (-1); }
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@ -219,10 +213,10 @@ main (int argc, char **argv)
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if (verbose)
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printf ("\nBacktrace across signal handler on alternate stack:\n");
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stk.ss_sp = malloc (STACK_SIZE);
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stk.ss_sp = malloc (SIGSTKSZ);
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if (!stk.ss_sp)
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panic ("failed to allocate SIGSTKSZ (%u) bytes\n", SIGSTKSZ);
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stk.ss_size = STACK_SIZE;
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stk.ss_size = SIGSTKSZ;
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stk.ss_flags = 0;
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if (sigaltstack (&stk, NULL) < 0)
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panic ("sigaltstack: %s\n", strerror (errno));
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