libbpf: workaround -Wmaybe-uninitialized false positive

Signed-off-by: Mike Pagano <mpagano@gentoo.org>

2 files changed, 71 insertions, 0 deletions

diff --git a/0000_README b/0000_README
index dae675f2..97b15896 100644
--- a/0000_README
+++ b/0000_README
@@ -495,6 +495,10 @@ Patch:  2960_jump-label-fix.patch
 From:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/
 Desc:   jump_label: Fix a regression
 
+Patch:  2990_libbpf-workaround-Wmaybe-uninitialized-false-pos.patch
+From:   https://lore.kernel.org/bpf/3ebbe7a4e93a5ddc3a26e2e11d329801d7c8de6b.1723217044.git.sam@gentoo.org/
+Desc:   libbpf: workaround -Wmaybe-uninitialized false positive
+
 Patch:  3000_Support-printing-firmware-info.patch
 From:   https://bugs.gentoo.org/732852
 Desc:   Print firmware info (Reqs CONFIG_GENTOO_PRINT_FIRMWARE_INFO). Thanks to Georgy Yakovlev
diff --git a/2990_libbpf-workaround-Wmaybe-uninitialized-false-pos.patch b/2990_libbpf-workaround-Wmaybe-uninitialized-false-pos.patch
new file mode 100644
index 00000000..86de18d7
--- /dev/null
+++ b/2990_libbpf-workaround-Wmaybe-uninitialized-false-pos.patch
@@ -0,0 +1,67 @@
+From git@z Thu Jan  1 00:00:00 1970
+Subject: [PATCH] libbpf: workaround -Wmaybe-uninitialized false positive
+From: Sam James <sam@gentoo.org>
+Date: Fri, 09 Aug 2024 16:24:04 +0100
+Message-Id: <3ebbe7a4e93a5ddc3a26e2e11d329801d7c8de6b.1723217044.git.sam@gentoo.org>
+MIME-Version: 1.0
+Content-Type: text/plain; charset="utf-8"
+Content-Transfer-Encoding: 8bit
+
+In `elf_close`, we get this with GCC 15 -O3 (at least):
+```
+In function ‘elf_close’,
+    inlined from ‘elf_close’ at elf.c:53:6,
+    inlined from ‘elf_find_func_offset_from_file’ at elf.c:384:2:
+elf.c:57:9: warning: ‘elf_fd.elf’ may be used uninitialized [-Wmaybe-uninitialized]
+   57 |         elf_end(elf_fd->elf);
+      |         ^~~~~~~~~~~~~~~~~~~~
+elf.c: In function ‘elf_find_func_offset_from_file’:
+elf.c:377:23: note: ‘elf_fd.elf’ was declared here
+  377 |         struct elf_fd elf_fd;
+      |                       ^~~~~~
+In function ‘elf_close’,
+    inlined from ‘elf_close’ at elf.c:53:6,
+    inlined from ‘elf_find_func_offset_from_file’ at elf.c:384:2:
+elf.c:58:9: warning: ‘elf_fd.fd’ may be used uninitialized [-Wmaybe-uninitialized]
+   58 |         close(elf_fd->fd);
+      |         ^~~~~~~~~~~~~~~~~
+elf.c: In function ‘elf_find_func_offset_from_file’:
+elf.c:377:23: note: ‘elf_fd.fd’ was declared here
+  377 |         struct elf_fd elf_fd;
+      |                       ^~~~~~
+```
+
+In reality, our use is fine, it's just that GCC doesn't model errno
+here (see linked GCC bug). Suppress -Wmaybe-uninitialized accordingly.
+
+Link: https://gcc.gnu.org/PR114952
+Signed-off-by: Sam James <sam@gentoo.org>
+---
+ tools/lib/bpf/elf.c | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c
+index c92e02394159e..ee226bb8e1af0 100644
+--- a/tools/lib/bpf/elf.c
++++ b/tools/lib/bpf/elf.c
+@@ -369,6 +369,9 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
+ 	return ret;
+ }
+ 
++#pragma GCC diagnostic push
++/* https://gcc.gnu.org/PR114952 */
++#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+ /* Find offset of function name in ELF object specified by path. "name" matches
+  * symbol name or name@@LIB for library functions.
+  */
+@@ -384,6 +387,7 @@ long elf_find_func_offset_from_file(const char *binary_path, const char *name)
+ 	elf_close(&elf_fd);
+ 	return ret;
+ }
++#pragma GCC diagnostic pop
+ 
+ struct symbol {
+ 	const char *name;
+-- 
+2.45.2
+