https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108045
Bug ID: 108045
Summary: analyzer: false positive memory leak
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: analyzer
Assignee: dmalcolm at gcc dot gnu.org
Reporter: jamie.bainbridge at gmail dot com
Target Milestone: ---
Created attachment 54060
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54060&action=edit
minimal reproducer
The analyzer detects a memory leak here, but I don't think there is one.
It seems not to have understood that I've kept the reference to "new_scr" (and
its child allocation) in the global "ctx->scr" when I swap the pointers on line
80/81 with:
struct screen_s *old_scr = ctx->scr;
ctx->scr = new_scr;
I found that if I omit the body of resize_screen() and place its instructions
directly in main(), then the analyzer doesn't report anything is wrong. It
seems the extra layer of indirection with the resize_screen() function trips it
up.
This problem happens with GCC 11.3.0, 12.1.0, and 13.0-20221209 nightly from
Compiler Explorer.
Full output from CE nightly below, using these options:
-v -save-temps -g3 -Og -std=c99 -Wall -Wextra -Wpedantic -fanalyzer
Using built-in specs.
COLLECT_GCC=/opt/compiler-explorer/gcc-snapshot/bin/gcc
Target: x86_64-linux-gnu
Configured with: ../gcc-trunk-20221209/configure
--prefix=/opt/compiler-explorer/gcc-build/staging --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu --disable-bootstrap
--enable-multiarch --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --enable-clocale=gnu
--enable-languages=c,c++,fortran,ada,objc,obj-c++,d --enable-ld=yes
--enable-gold=yes --enable-libstdcxx-debug --enable-libstdcxx-time=yes
--enable-linker-build-id --enable-lto --enable-plugins --enable-threads=posix
--with-pkgversion=Compiler-Explorer-Build-gcc-e6110da479951b759a12c5618f5304187b650326-binutils-2.38
--enable-libstdcxx-backtrace=yes
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.0.0 20221209 (experimental)
(Compiler-Explorer-Build-gcc-e6110da479951b759a12c5618f5304187b650326-binutils-2.38)
COLLECT_GCC_OPTIONS='-fdiagnostics-color=always' '-g' '-o' '/app/output.s'
'-masm=intel' '-S' '-v' '-save-temps' '-g3' '-Og' '-std=c99' '-Wall' '-Wextra'
'-Wpedantic' '-fanalyzer' '-mtune=generic' '-march=x86-64' '-dumpdir' '/app/'
/opt/compiler-explorer/gcc-trunk-20221209/bin/../libexec/gcc/x86_64-linux-gnu/13.0.0/cc1
-E -quiet -v -imultiarch x86_64-linux-gnu -iprefix
/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/x86_64-linux-gnu/13.0.0/
-dD <source> -masm=intel -mtune=generic -march=x86-64 -std=c99 -Wall -Wextra
-Wpedantic -fdiagnostics-color=always -fanalyzer -g -g3 -fworking-directory -Og
-fpch-preprocess -o /app/output.i
ignoring nonexistent directory
"/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/x86_64-linux-gnu/13.0.0/../../../../x86_64-linux-gnu/include"
ignoring duplicate directory
"/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/13.0.0/include"
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring duplicate directory
"/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/13.0.0/include-fixed/x86_64-linux-gnu"
ignoring duplicate directory
"/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/13.0.0/include-fixed"
ignoring nonexistent directory
"/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/13.0.0/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/x86_64-linux-gnu/13.0.0/include
/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/x86_64-linux-gnu/13.0.0/include-fixed/x86_64-linux-gnu
/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/x86_64-linux-gnu/13.0.0/include-fixed
/usr/local/include
/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/../../include
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-fdiagnostics-color=always' '-g' '-o' '/app/output.s'
'-masm=intel' '-S' '-v' '-save-temps' '-g3' '-Og' '-std=c99' '-Wall' '-Wextra'
'-Wpedantic' '-fanalyzer' '-mtune=generic' '-march=x86-64' '-dumpdir' '/app/'
/opt/compiler-explorer/gcc-trunk-20221209/bin/../libexec/gcc/x86_64-linux-gnu/13.0.0/cc1
-fpreprocessed /app/output.i -quiet -dumpdir /app/ -dumpbase output.c
-dumpbase-ext .c -masm=intel -mtune=generic -march=x86-64 -g -g3 -Og -Wall
-Wextra -Wpedantic -std=c99 -version -fdiagnostics-color=always -fanalyzer -o
/app/output.s
GNU C99
(Compiler-Explorer-Build-gcc-e6110da479951b759a12c5618f5304187b650326-binutils-2.38)
version 13.0.0 20221209 (experimental) (x86_64-linux-gnu)
compiled by GNU C version 9.4.0, GMP version 6.2.1, MPFR version 4.1.0,
MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
GNU C99
(Compiler-Explorer-Build-gcc-e6110da479951b759a12c5618f5304187b650326-binutils-2.38)
version 13.0.0 20221209 (experimental) (x86_64-linux-gnu)
compiled by GNU C version 9.4.0, GMP version 6.2.1, MPFR version 4.1.0,
MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: 18c5716274d15bcd60b31c3cdaf8ef4d
<source>: In function 'screen_destroy':
<source>:67:9: warning: leak of '<unknown>' [CWE-401] [-Wanalyzer-malloc-leak]
67 | free(scr);
| ^~~~~~~~~
'resize_screen': event 1
|
| 70 | void resize_screen(size_t cols, size_t rows)
| | ^~~~~~~~~~~~~
| | |
| | (1) entry to 'resize_screen'
|
'resize_screen': event 2
|
|<source>:74:19:
| 74 | new_scr = screen_create(cols, rows);
| | ^~~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (2) calling 'screen_create' from 'resize_screen'
|
+--> 'screen_create': event 3
|
|<source>:27:18:
| 27 | struct screen_s *screen_create(size_t cols, size_t rows)
| | ^~~~~~~~~~~~~
| | |
| | (3) entry to 'screen_create'
|
'screen_create': event 4
|
|<source>:32:12:
| 32 | if (!result)
| | ^
| | |
| | (4) following 'false' branch (when 'result' is
non-NULL)...
|
'screen_create': events 5-8
|
|<source>:35:9:
| 35 | result->cols = cols;
| | ^~~~~~
| | |
| | (5) ...to here
|......
| 39 | result->data = calloc(rows, sizeof(result->data) +
sizeof(*result->data) * cols);
| |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (6) allocated here
| 40 | if (!result->data) {
| | ~
| | |
| | (7) assuming 'calloc(rows, (cols + 1) * 8)' is
non-NULL
| | (8) following 'false' branch...
|
'screen_create': events 9-10
|
|<source>:46:9:
| 46 | char *ptr = (char *)(result->data + rows);
| | ^~~~
| | |
| | (9) ...to here
|......
| 49 | for (size_t row = 0; row < rows; row++)
| | ~~~~~~~~~~
| | |
| | (10) following 'false'
branch (when 'row >= rows')...
|
'screen_create': event 11
|
|cc1:
| (11): ...to here
|
<------+
|
'resize_screen': events 12-15
|
|<source>:74:19:
| 74 | new_scr = screen_create(cols, rows);
| | ^~~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (12) returning to 'resize_screen' from
'screen_create'
| 75 | if (!new_scr) {
| | ~
| | |
| | (13) following 'false' branch (when 'new_scr' is
non-NULL)...
|......
| 80 | struct screen_s *old_scr = ctx->scr;
| | ~~~~~~
| | |
| | (14) ...to here
|......
| 86 | screen_destroy(old_scr);
| | ~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (15) calling 'screen_destroy' from 'resize_screen'
|
+--> 'screen_destroy': events 16-18
|
|<source>:56:6:
| 56 | void screen_destroy(struct screen_s *scr)
| | ^~~~~~~~~~~~~~
| | |
| | (16) entry to 'screen_destroy'
| 57 | {
| 58 | if (!scr)
| | ~
| | |
| | (17) following 'false' branch (when 'scr' is
non-NULL)...
|......
| 61 | free(scr->data);
| | ~~~~
| | |
| | (18) ...to here
|
'screen_destroy': event 19
|
|<source>:67:9:
| 67 | free(scr);
| | ^~~~~~~~~
| | |
| | (19) '<unknown>' leaks here; was allocated at (6)
|
COMPILER_PATH=/opt/compiler-explorer/gcc-trunk-20221209/bin/../libexec/gcc/x86_64-linux-gnu/13.0.0/:/opt/compiler-explorer/gcc-trunk-20221209/bin/../libexec/gcc/x86_64-linux-gnu/:/opt/compiler-explorer/gcc-trunk-20221209/bin/../libexec/gcc/:/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/x86_64-linux-gnu/13.0.0/../../../../x86_64-linux-gnu/bin/
LIBRARY_PATH=/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/x86_64-linux-gnu/13.0.0/:/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/x86_64-linux-gnu/:/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/:/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/x86_64-linux-gnu/13.0.0/../../../../lib64/:/lib/x86_64-linux-gnu/:/lib/../lib64/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib64/:/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/x86_64-linux-gnu/13.0.0/../../../../x86_64-linux-gnu/lib/:/opt/compiler-explorer/gcc-trunk-20221209/bin/../lib/gcc/x86_64-linux-gnu/13.0.0/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-fdiagnostics-color=always' '-g' '-o' '/app/output.s'
'-masm=intel' '-S' '-v' '-save-temps' '-g3' '-Og' '-std=c99' '-Wall' '-Wextra'
'-Wpedantic' '-fanalyzer' '-mtune=generic' '-march=x86-64' '-dumpdir'
'/app/output.'
Compiler returned: 0
