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The `__monstartup()` allocates a buffer used to store all the data accumulated by the monitor. The size of this buffer depends on the size of the internal structures used and the address range for which the monitor is activated, as well as on the maximum density of call instructions and/or callable functions that could be potentially on a segment of executable code. In particular a hash table of arcs is placed at the end of this buffer. The size of this hash table is calculated in bytes as p->fromssize = p->textsize / HASHFRACTION; but actually should be p->fromssize = ROUNDUP(p->textsize / HASHFRACTION, sizeof(*p->froms)); This results in writing beyond the end of the allocated buffer when an added arc corresponds to a call near from the end of the monitored address range, since `_mcount()` check the incoming caller address for monitored range but not the intermediate result hash-like index that uses to write into the table. It should be noted that when the results are output to `gmon.out`, the table is read to the last element calculated from the allocated size in bytes, so the arcs stored outside the buffer boundary did not fall into `gprof` for analysis. Thus this "feature" help me to found this bug during working with https://sourceware.org/bugzilla/show_bug.cgi?id=29438 Just in case, I will explicitly note that the problem breaks the `make test t=gmon/tst-gmon-dso` added for Bug 29438. There, the arc of the `f3()` call disappears from the output, since in the DSO case, the call to `f3` is located close to the end of the monitored range. Signed-off-by: Леонид Юрьев (Leonid Yuriev) <leo@yuriev.ru> Another minor error seems a related typo in the calculation of `kcountsize`, but since kcounts are smaller than froms, this is actually to align the p->froms data. Co-authored-by: DJ Delorie <dj@redhat.com> Reviewed-by: Carlos O'Donell <carlos@redhat.com> |
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This directory contains the sources of the GNU C Library. See the file "version.h" for what release version you have. The GNU C Library is the standard system C library for all GNU systems, and is an important part of what makes up a GNU system. It provides the system API for all programs written in C and C-compatible languages such as C++ and Objective C; the runtime facilities of other programming languages use the C library to access the underlying operating system. In GNU/Linux systems, the C library works with the Linux kernel to implement the operating system behavior seen by user applications. In GNU/Hurd systems, it works with a microkernel and Hurd servers. The GNU C Library implements much of the POSIX.1 functionality in the GNU/Hurd system, using configurations i[4567]86-*-gnu. When working with Linux kernels, this version of the GNU C Library requires Linux kernel version 3.2 or later. Also note that the shared version of the libgcc_s library must be installed for the pthread library to work correctly. The GNU C Library supports these configurations for using Linux kernels: aarch64*-*-linux-gnu alpha*-*-linux-gnu arc*-*-linux-gnu arm-*-linux-gnueabi csky-*-linux-gnuabiv2 hppa-*-linux-gnu i[4567]86-*-linux-gnu x86_64-*-linux-gnu Can build either x86_64 or x32 ia64-*-linux-gnu loongarch64-*-linux-gnu Hardware floating point, LE only. m68k-*-linux-gnu microblaze*-*-linux-gnu mips-*-linux-gnu mips64-*-linux-gnu or1k-*-linux-gnu powerpc-*-linux-gnu Hardware or software floating point, BE only. powerpc64*-*-linux-gnu Big-endian and little-endian. s390-*-linux-gnu s390x-*-linux-gnu riscv32-*-linux-gnu riscv64-*-linux-gnu sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu If you are interested in doing a port, please contact the glibc maintainers; see https://www.gnu.org/software/libc/ for more information. See the file INSTALL to find out how to configure, build, and install the GNU C Library. You might also consider reading the WWW pages for the C library at https://www.gnu.org/software/libc/. The GNU C Library is (almost) completely documented by the Texinfo manual found in the `manual/' subdirectory. The manual is still being updated and contains some known errors and omissions; we regret that we do not have the resources to work on the manual as much as we would like. For corrections to the manual, please file a bug in the `manual' component, following the bug-reporting instructions below. Please be sure to check the manual in the current development sources to see if your problem has already been corrected. Please see https://www.gnu.org/software/libc/bugs.html for bug reporting information. We are now using the Bugzilla system to track all bug reports. This web page gives detailed information on how to report bugs properly. The GNU C Library is free software. See the file COPYING.LIB for copying conditions, and LICENSES for notices about a few contributions that require these additional notices to be distributed. License copyright years may be listed using range notation, e.g., 1996-2015, indicating that every year in the range, inclusive, is a copyrightable year that would otherwise be listed individually.