[LTP] [PATCH 1/1] shmctl03: Fix shmall clamped to UINT32_MAX in 32bit compat mode

[Petr Vorel]

Unlike shmmax, the kernel's compat shmctl(IPC_INFO) path does not clamp
shmall but truncates the 64-bit value into the 32-bit compat shminfo
(see copy_compat_shminfo_to_user() in ipc/shm.c, originally changed by
af7c693f14606 ("Cap shmmax at INT_MAX in compat shminfo") in kernel
v2.6.22.

Parsing /proc/sys/kernel/shmall's full decimal value with "%lu" into a
32-bit unsigned long saturates to ULONG_MAX instead of truncating,
causing a mismatch. Read it into an unsigned long long and compare
against the low 32 bits in compat mode.

Because this is a test specific error, fix it in the test itself instead
adding support to the LTP library.

This fixes error:

    shmctl03.c:35: TFAIL: /proc/sys/kernel/shmall != 4294967040 got 4294967295

Reported-by: Wei Gao <wegao@suse.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
---
Hi,

yet another attempt to fix struct shminfo shmall.
I believe in the end this is better than a general approach I posted
previously based on Andrea's suggestion [1] or older Wei's approach [2][3]
based on Cyril's suggestion.

Kind regards,
Petr

[1] https://patchwork.kernel.org/project/ltp/patch/20260924112514.2375626-2-pvorel@suse.cz/
[2] https://patchwork.kernel.org/project/ltp/patch/20260903095255.4925-3-wegao@suse.com/
[3] https://patchwork.kernel.org/project/ltp/patch/20260903095255.4925-2-wegao@suse.com/

 testcases/kernel/syscalls/shmctl/shmctl03.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/testcases/kernel/syscalls/shmctl/shmctl03.c b/testcases/kernel/syscalls/shmctl/shmctl03.c
index bccab5ba37..e5937fd023 100644
--- a/testcases/kernel/syscalls/shmctl/shmctl03.c
+++ b/testcases/kernel/syscalls/shmctl/shmctl03.c
@@ -18,6 +18,7 @@ static void verify_ipcinfo(void)
 {
 	struct shminfo info;
 	unsigned long shmmax;
+	unsigned long long shmall;
 
 	TST_EXP_POSITIVE(shmctl(0, IPC_INFO, (struct shmid_ds *)&info));
 	if (!TST_PASS)
@@ -32,7 +33,18 @@ static void verify_ipcinfo(void)
 		TST_EXP_EQ_LU(info.shmmax, shmmax);
 
 	TST_ASSERT_ULONG(PATH_KERN_SHMMNI, info.shmmni);
-	TST_ASSERT_ULONG(PATH_KERN_SHMALL, info.shmall);
+
+	/*
+	 * On 32-bit compat, the kernel truncates the (64-bit) shmall to the
+	 * 32-bit compat shminfo, instead of clamping it like shmmax. The
+	 * /proc file still holds the untruncated value, so compare against
+	 * its low 32 bits.
+	 */
+	SAFE_FILE_SCANF(PATH_KERN_SHMALL, "%llu", &shmall);
+	if (tst_is_compat_mode())
+		TST_EXP_EQ_LU(info.shmall, (uint32_t)shmall);
+	else
+		TST_EXP_EQ_LU(info.shmall, shmall);
 }
 
 static struct tst_test test = {
-- 
2.56.0