[PATCH] async_die_is_recursing: fix use of pthread_getspecific for Fedora

["Victoria Dye via GitGitGadget" <gitgitgadget@gmail.com>]

From: Victoria Dye <vdye@github.com>

Correct an issue encountered in the `dockerized(pedantic, fedora)` CI build,
first appearing after the release of v36 as the latest stable version of the
Fedora docker image. This image includes a version of `glibc` with the
attribute `__attr_access_none` added to `pthread_getspecific` [1], the
implementation of which only exists for GCC 11.X - the version included in
Fedora. The attribute requires that the pointer provided in the second
argument of `pthread_getspecific` must, if not NULL, be a pointer to a valid
object. In the usage in `async_die_is_recursing`, `(void *)1` is not valid,
resulting in the error.

The fix imitates a workaround added in SELinux [2] by using the pointer to
`ret` as the second argument to `pthread_getspecific`. This guaranteed
non-NULL, valid pointer adheres to the current intended usage of
`pthread_getspecific` while not triggering the build error.

[1] https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=a1561c3bbe8
[2] https://lore.kernel.org/all/20211021140519.6593-1-cgzones@googlemail.com/

Co-authored-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Victoria Dye <vdye@github.com>
---
    async_die_is_recursing: fix use of pthread_getspecific for Fedora
    
    Following up on Johannes' report earlier [1], this patch fixes a
    compiler error in the Fedora CI build (the same issue was identified in
    a local developer build about a week ago [2]). This fix changes the
    second argument in the call to pthread_getspecific from '(void *)1' to a
    valid pointer, thus preventing the error in the use of
    __attr_access_none.
    
    [1]
    https://lore.kernel.org/git/nycvar.QRO.7.76.6.2111040007170.56@tvgsbejvaqbjf.bet/
    [2]
    https://lore.kernel.org/git/43fe6d5c-bdb2-585c-c601-1da7a1b3ff8b@archlinux.org/

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1072%2Fvdye%2Ffix-fedora-build-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1072/vdye/fix-fedora-build-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1072

 run-command.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/run-command.c b/run-command.c
index 7ef5cc712a9..a82cf69e7d3 100644
--- a/run-command.c
+++ b/run-command.c
@@ -1099,7 +1099,7 @@ static NORETURN void die_async(const char *err, va_list params)
 static int async_die_is_recursing(void)
 {
 	void *ret = pthread_getspecific(async_die_counter);
-	pthread_setspecific(async_die_counter, (void *)1);
+	pthread_setspecific(async_die_counter, &ret); /* set to any non-NULL valid pointer */
 	return ret != NULL;
 }
 

base-commit: 876b1423317071f43c99666f3fc3db3642dfbe14
-- 
gitgitgadget