Debug: enable kernel boot up time measurement #11
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To measure kernel boot up time, reserved region in pl011 is used as trap MMIO region to record kernel boot timestamp. For now, we trap at 2 point: the first is nearly the first instruction of kernel start; the second is just before call the init bin for userspace. These 2 points can cover the whole kernel boot time. If there is no pl011, the first write is still there but the second won't happen. Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
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Hi @rbradford, me and @michael2012z would suggest that maybe we can review this PR and cloud-hypervisor/cloud-hypervisor#3838 at the same time to minimize the side effect to our CI :) I will give both a test first - but from the CI in the cloud hypervisor repo, this time the kernel change looks fine. |
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By checking CI in cloud-hypervisor/cloud-hypervisor#3838, this time the kernel patch will not break CI. |
MrXinWang
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Mar 17, 2022
rbradford
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Jan 14, 2025
[ Upstream commit 5bf1557 ] test_progs uses glibc specific functions backtrace() and backtrace_symbols_fd() to print backtrace in case of SIGSEGV. Recent commit (see fixes) updated test_progs.c to define stub versions of the same functions with attriubte "weak" in order to allow linking test_progs against musl libc. Unfortunately this broke the backtrace handling for glibc builds. As it turns out, glibc defines backtrace() and backtrace_symbols_fd() as weak: $ llvm-readelf --symbols /lib64/libc.so.6 \ | grep -P '( backtrace_symbols_fd| backtrace)$' 4910: 0000000000126b40 161 FUNC WEAK DEFAULT 16 backtrace 6843: 0000000000126f90 852 FUNC WEAK DEFAULT 16 backtrace_symbols_fd So does test_progs: $ llvm-readelf --symbols test_progs \ | grep -P '( backtrace_symbols_fd| backtrace)$' 2891: 00000000006ad190 15 FUNC WEAK DEFAULT 13 backtrace 11215: 00000000006ad1a0 41 FUNC WEAK DEFAULT 13 backtrace_symbols_fd In such situation dynamic linker is not obliged to favour glibc implementation over the one defined in test_progs. Compiling with the following simple modification to test_progs.c demonstrates the issue: $ git diff ... \--- a/tools/testing/selftests/bpf/test_progs.c \+++ b/tools/testing/selftests/bpf/test_progs.c \@@ -1817,6 +1817,7 @@ int main(int argc, char **argv) if (err) return err; + *(int *)0xdeadbeef = 42; err = cd_flavor_subdir(argv[0]); if (err) return err; $ ./test_progs [0]: Caught signal #11! Stack trace: <backtrace not supported> Segmentation fault (core dumped) Resolve this by hiding stub definitions behind __GLIBC__ macro check instead of using "weak" attribute. Fixes: c9a83e7 ("selftests/bpf: Fix compile if backtrace support missing in libc") Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Tested-by: Tony Ambardar <tony.ambardar@gmail.com> Reviewed-by: Tony Ambardar <tony.ambardar@gmail.com> Acked-by: Daniel Xu <dxu@dxuuu.xyz> Link: https://lore.kernel.org/bpf/20241003210307.3847907-1-eddyz87@gmail.com Signed-off-by: Sasha Levin <sashal@kernel.org>
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To measure kernel boot up time, reserved region in pl011 is used as trap
MMIO region to record kernel boot timestamp.
For now, we trap at 2 point: the first is nearly the first instruction of
kernel start; the second is just before call the init bin for userspace.
These 2 points can cover the whole kernel boot time.
If there is no pl011, the first write is still there but the second
won't happen.
Signed-off-by: Jianyong Wu jianyong.wu@arm.com