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Théophile Bastian 2018-08-17 20:38:20 +02:00
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report/report.tex
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@ -55,8 +55,8 @@ Under supervision of Francesco Zappa-Nardelli\\
\subsection*{Source code}\label{ssec:source_code} \subsection*{Source code}\label{ssec:source_code}
The source code of all the implementations made during this internship is The source code of all the implementations made during this internship is
available at \url{https://git.tobast.fr/m2-internship/} under free software available at \url{https://git.tobast.fr/m2-internship/}. See
licenses, in various repositories. Section~\ref{ssec:code_avail} for details.
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@ -679,6 +679,16 @@ The tentative approach that was chosen to try to get better unwinding speeds at
a reasonable space loss was to compile directly the \ehframe{} into native a reasonable space loss was to compile directly the \ehframe{} into native
machine code on the x86\_64 platform. machine code on the x86\_64 platform.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Code availability}\label{ssec:code_avail}
All the code produced during this internship is available on the various
repositories from \url{https://git.tobast.fr/m2-internship/}. The repositories
contain \texttt{README} files describing them; a summary and global description
can be found in the \texttt{abstract} repository. This should be detailed
enough to run the project. The source code is entirely under free software
licenses.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Compilation: \ehelfs}\label{ssec:ehelfs} \subsection{Compilation: \ehelfs}\label{ssec:ehelfs}
@ -748,6 +758,16 @@ imagine, in a future environment production, packaging \ehelfs{} files
separately, so that people interested in heavy computation can have the choice separately, so that people interested in heavy computation can have the choice
to install them. to install them.
This, in particular, means that each ELF file has its unwinding data in a
separate \ehelf{} file --~just like with DWARF, where each ELF retains its own
DWARF data. Thus, an unwinder must first acquire a \emph{memory map}, a table
listing the various ELF files loaded and \emph{mapped} in memory, and on which
memory segment. This memory map is provided by the operating system --~for
instance, on Linux, it is available as a file in \texttt{/proc}. Once this map
is acquired, when unwinding from a given IP, the unwinder must identify the
memory segment from which it comes, deduce the source ELF file, and deduce the
corresponding \ehelf.
\medskip \medskip
\lstinputlisting[language=C, caption={\ehelf{} for the previous example}, \lstinputlisting[language=C, caption={\ehelf{} for the previous example},
@ -922,14 +942,13 @@ Interfacing \ehelfs{} with \prog{perf} required, in a first place, to fork
turned out necessary to slightly modify \prog{libunwind}'s interface to add a turned out necessary to slightly modify \prog{libunwind}'s interface to add a
parameter to an initialisation function, since \prog{libunwind} is made to be parameter to an initialisation function, since \prog{libunwind} is made to be
agnostic of the system and process as much as possible, to be able to unwind in agnostic of the system and process as much as possible, to be able to unwind in
any context. This very restricted information lacked a \emph{memory map}, a any context. This very restricted information lacked a memory map (see
table indicating which shared object is mapped at which address in memory, in Section~\ref{ssec:ehelfs}) in order to use \ehelfs. Apart from this, the
order to use \ehelfs. Apart from this, the modified version of \prog{libunwind} modified version of \prog{libunwind} produced is entirely compatible with the
produced is entirely compatible with the vanilla version. This means that the vanilla version. This means that the only modifications required to use
only modifications required to use \ehelfs{} within any project using \ehelfs{} within any project using \prog{libunwind} should be changing one line
\prog{libunwind} should be changing one line of code to add one parameter to a of code to add one parameter to a function call and linking against the
function call and linking against the modified version of \prog{libunwind} modified version of \prog{libunwind} instead of the system version.
instead of the system version.
Once this was done, plugging it in \prog{perf} was the matter of a few lines of Once this was done, plugging it in \prog{perf} was the matter of a few lines of
code only, left apart the benchmarking code. The major problem encountered was code only, left apart the benchmarking code. The major problem encountered was
@ -1212,8 +1231,9 @@ some unsupported instruction at all.
\hfill \begin{minipage}{0.7\textwidth} \hfill \begin{minipage}{0.7\textwidth}
\begin{flushright} \begin{flushright}
\itshape{} \small{} \itshape{} \small{}
Unless otherwise explicitly stated, any image, source code snippet or Unless otherwise explicitly stated, any image from the present document
table from the present document can be reused freely by anyone. is distributed under Creative Commons BY-SA license, and any code
snippet is distributed under 3-clause BSD license.
\end{flushright} \end{flushright}
\end{minipage} \end{minipage}