From 85e4f762c224c52708919a10c9fa5b79e7949564 Mon Sep 17 00:00:00 2001 From: Elijah Newren Date: Wed, 19 Mar 2025 16:22:57 +0000 Subject: [PATCH] ci: add build checking for side-effects in assert() calls It is a big no-no to have side-effects in an assertion, because if the assert() is compiled out, you don't get that side-effect, leading to the code behaving differently. That can be a large headache to debug. We have roughly 566 assert() calls in our codebase (my grep might have picked up things that aren't actually assert() calls, but most appeared to be). All but 9 of them can be determined by gcc to be free of side effects with a clever redefine of assert() provided by Bruno De Fraine (from https://stackoverflow.com/questions/10593492/catching-assert-with-side-effects), who upon request has graciously placed his two-liner into the public domain without warranty of any kind. The current 9 assert() calls flagged by this clever redefinition of assert() appear to me to be free of side effects as well, but are too complicated for a compiler/linker to figure that since each assertion involves some kind of function call. Add a CI job which will find and report these possibly problematic assertions, and have the job suggest to the user that they replace these with ASSERT() calls. Example output from running: ``` ERROR: The compiler could not verify the following assert() calls are free of side-effects. Please replace with ASSERT() calls. /home/newren/floss/git/diffcore-rename.c:1409 assert(!dir_rename_count || strmap_empty(dir_rename_count)); /home/newren/floss/git/merge-ort.c:1645 assert(renames->deferred[side].trivial_merges_okay && !strset_contains(&renames->deferred[side].target_dirs, path)); /home/newren/floss/git/merge-ort.c:794 assert(omittable_hint == (!starts_with(type_short_descriptions[type], "CONFLICT") && !starts_with(type_short_descriptions[type], "ERROR")) || type == CONFLICT_DIR_RENAME_SUGGESTED); /home/newren/floss/git/merge-recursive.c:1200 assert(!merge_remote_util(commit)); /home/newren/floss/git/object-file.c:2709 assert(would_convert_to_git_filter_fd(istate, path)); /home/newren/floss/git/parallel-checkout.c:280 assert(is_eligible_for_parallel_checkout(pc_item->ce, &pc_item->ca)); /home/newren/floss/git/scalar.c:244 assert(have_fsmonitor_support()); /home/newren/floss/git/scalar.c:254 assert(have_fsmonitor_support()); /home/newren/floss/git/sequencer.c:4968 assert(!(opts->signoff || opts->no_commit || opts->record_origin || should_edit(opts) || opts->committer_date_is_author_date || opts->ignore_date)); ``` Note that if there are possibly problematic assertions, not necessarily all of them will be shown in a single run, because the compiler errors may include something like "ld: ... more undefined references to `not_supposed_to_survive' follow" instead of listing each individually. But in such cases, once you clean up a few that are shown in your first run, subsequent runs will show (some of) the ones that remain, allowing you to iteratively remove them all. Helped-by: Bruno De Fraine Signed-off-by: Elijah Newren Acked-by: Taylor Blau Signed-off-by: Junio C Hamano --- Makefile | 4 ++++ ci/check-unsafe-assertions.sh | 18 ++++++++++++++++++ ci/run-static-analysis.sh | 2 ++ git-compat-util.h | 6 ++++++ 4 files changed, 30 insertions(+) create mode 100755 ci/check-unsafe-assertions.sh diff --git a/Makefile b/Makefile index 7315507381..57774912f1 100644 --- a/Makefile +++ b/Makefile @@ -2261,6 +2261,10 @@ ifdef WITH_BREAKING_CHANGES BASIC_CFLAGS += -DWITH_BREAKING_CHANGES endif +ifdef CHECK_ASSERTION_SIDE_EFFECTS + BASIC_CFLAGS += -DCHECK_ASSERTION_SIDE_EFFECTS +endif + ifdef INCLUDE_LIBGIT_RS # Enable symbol hiding in contrib/libgit-sys/libgitpub.a without making # us rebuild the whole tree every time we run a Rust build. diff --git a/ci/check-unsafe-assertions.sh b/ci/check-unsafe-assertions.sh new file mode 100755 index 0000000000..233bd9dfbc --- /dev/null +++ b/ci/check-unsafe-assertions.sh @@ -0,0 +1,18 @@ +#!/bin/sh + +make CHECK_ASSERTION_SIDE_EFFECTS=1 >compiler_output 2>compiler_error +if test $? != 0 +then + echo >&2 "ERROR: The compiler could not verify the following assert()" + echo >&2 " calls are free of side-effects. Please replace with" + echo >&2 " ASSERT() calls." + grep undefined.reference.to..not_supposed_to_survive compiler_error | + sed -e s/:[^:]*$// | sort | uniq | tr ':' ' ' | + while read f l + do + printf "${f}:${l}\n " + awk -v start="$l" 'NR >= start { print; if (/\);/) exit }' $f + done + exit 1 +fi +rm compiler_output compiler_error diff --git a/ci/run-static-analysis.sh b/ci/run-static-analysis.sh index 0d51e5ce0e..ae714e020a 100755 --- a/ci/run-static-analysis.sh +++ b/ci/run-static-analysis.sh @@ -31,4 +31,6 @@ exit 1 make check-pot +${0%/*}/check-unsafe-assertions.sh + save_good_tree diff --git a/git-compat-util.h b/git-compat-util.h index d7f3407128..5891efaeb1 100644 --- a/git-compat-util.h +++ b/git-compat-util.h @@ -1585,4 +1585,10 @@ static inline void *container_of_or_null_offset(void *ptr, size_t offset) ((uintptr_t)&(ptr)->member - (uintptr_t)(ptr)) #endif /* !__GNUC__ */ +#ifdef CHECK_ASSERTION_SIDE_EFFECTS +#undef assert +extern int not_supposed_to_survive; +#define assert(expr) ((void)(not_supposed_to_survive || (expr))) +#endif /* CHECK_ASSERTION_SIDE_EFFECTS */ + #endif -- 2.47.3