Hi Kevin,
On 21/11/2022 16:44, Kevin Brodsky wrote:
On 18/11/2022 19:39, Teo Couprie Diaz wrote:
Direct usage of brk is discouraged in favor of using malloc. Also, brk was removed from POSIX in POSIX.1-2001. In particular, the musl libc's brk always returns -ENOMEM which causes the LTP tests to prematurely. Invoking the syscall directly allows them to
*exit* prematurely?
Correct, I did forget it.
properly validate brk behavior.
Instead, use tst_syscall() and handle the failure cases ourselves, as
I think s/Instead,// as you have already introduced that idea in the previous sentence.
That does sound better, thanks.
we don't depend on the libc to do it anymore.
The patch also removes the dependency on sbrk to get the current break as it has the same issues. Instead, call tst_syscall(__NR_brk, 0) which should always fail, returning the current break.
I think it can't both fail and return the current break :) Probably remove "which should always fail", or maybe s/always/never/?
Well, from my understanding that's exactly the expected behavior ! From the man page BRK(2):
[...], the actual Linux system call returns the new program break on success. *On
failure, the
system call returns the current break.* The glibc wrapper
function does
some work (i.e., checks whether the new break is less than
addr) to
provide the 0 and -1 return values described above.
Also in mm/mmap.c, at the end of SYSCALL_DEFINE1(brk, unsigned long, brk) :
out: mmap_write_unlock(mm); return origbrk;
Where origbrk is saved at the beginning and out is jumped to whenever there is an error.
So making a brk syscall with 0 should always fail (it's smaller than the minimum break), and also return the current(/original ?) break unchanged.
But maybe I am misunderstanding your comment itself ? Please let me know !
Aside from that the code looks good to me, and so does patch 2.
Kevin
Thanks for the review Kevin ! Regards, Téo
Signed-off-by: Teo Couprie Diaz teo.coupriediaz@arm.com
testcases/kernel/syscalls/brk/brk01.c | 13 +++++-------- testcases/kernel/syscalls/brk/brk02.c | 14 ++++++-------- 2 files changed, 11 insertions(+), 16 deletions(-)
diff --git a/testcases/kernel/syscalls/brk/brk01.c b/testcases/kernel/syscalls/brk/brk01.c index 5f482b943..d4596c20f 100644 --- a/testcases/kernel/syscalls/brk/brk01.c +++ b/testcases/kernel/syscalls/brk/brk01.c @@ -9,14 +9,15 @@ #include <errno.h> #include "tst_test.h" +#include "lapi/syscalls.h" void verify_brk(void) {
- uintptr_t cur_brk, new_brk;
- void *cur_brk, *new_brk; size_t inc = getpagesize() * 2 - 1; unsigned int i;
- cur_brk = (uintptr_t)sbrk(0);
- cur_brk = (void *)tst_syscall(__NR_brk, 0);
for (i = 0; i < 33; i++) { switch (i % 3) { @@ -31,16 +32,12 @@ void verify_brk(void) break; }
TST_EXP_PASS_SILENT(brk((void *)new_brk), "brk()");if (!TST_PASS)return;cur_brk = (uintptr_t)sbrk(0);
cur_brk = (void *)tst_syscall(__NR_brk, new_brk);if (cur_brk != new_brk) { tst_res(TFAIL, "brk() failed to set address have %p expected %p",
(void *)cur_brk, (void *)new_brk);
cur_brk, new_brk); return;diff --git a/testcases/kernel/syscalls/brk/brk02.c b/testcases/kernel/syscalls/brk/brk02.c index 11e803cb4..dabda30c2 100644 --- a/testcases/kernel/syscalls/brk/brk02.c +++ b/testcases/kernel/syscalls/brk/brk02.c @@ -14,24 +14,22 @@ #include <unistd.h> #include <sys/mman.h> #include "tst_test.h" +#include "lapi/syscalls.h" void brk_down_vmas(void) {
- void *brk_addr = sbrk(0);
- if (brk_addr == (void *) -1)
tst_brk(TBROK, "sbrk() failed");
- void *brk_addr = (void *)tst_syscall(__NR_brk, 0);
unsigned long page_size = getpagesize(); void *addr = brk_addr + page_size;
- if (brk(addr)) {
- if ((void *)tst_syscall(__NR_brk, addr) < addr) { tst_res(TFAIL | TERRNO, "Cannot expand brk() by page size"); return; }
addr += page_size;
- if (brk(addr)) {
- if ((void *)tst_syscall(__NR_brk, addr) < addr) { tst_res(TFAIL | TERRNO, "Cannot expand brk() by 2x page size"); return; }
@@ -42,12 +40,12 @@ void brk_down_vmas(void) } addr += page_size;
- if (brk(addr)) {
- if ((void *)tst_syscall(__NR_brk, addr) < addr) { tst_res(TFAIL | TERRNO, "Cannot expand brk() after mprotect"); return; }
- if (brk(brk_addr)) {
- if ((void *)tst_syscall(__NR_brk, brk_addr) != brk_addr) { tst_res(TFAIL | TERRNO, "Cannot restore brk() to start address"); return; }
base-commit: 75fda47a48d1b6f1c6671fa9819ca9fd9169cf2a
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