sysconf(_SC_ARG_MAX): go back to imitating the kernel.
For reasons explained in the code comment, go back to roughly our old
code. The "new" tests are just the old tests resurrected.
This also passes the current toybox xargs tests, which were the
motivation for going back on our earlier decision.
Test: bionic and toybox tests
Change-Id: I33cbcc04107efe81fdbc8166dc9ae844e471173e
diff --git a/tests/unistd_test.cpp b/tests/unistd_test.cpp
index 99d92e6..f3b08c3 100644
--- a/tests/unistd_test.cpp
+++ b/tests/unistd_test.cpp
@@ -27,6 +27,7 @@
#include <stdint.h>
#include <sys/capability.h>
#include <sys/param.h>
+#include <sys/resource.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/utsname.h>
@@ -1065,11 +1066,38 @@
}
TEST(UNISTD_TEST, sysconf_SC_ARG_MAX) {
- // https://lkml.org/lkml/2017/11/15/813.
-#if !defined(ARG_MAX)
-#define ARG_MAX 131072
-#endif
- ASSERT_EQ(ARG_MAX, sysconf(_SC_ARG_MAX));
+ // Since Linux 2.6.23, ARG_MAX isn't a constant and depends on RLIMIT_STACK.
+ // See prepare_arg_pages() in the kernel for the gory details:
+ // https://elixir.bootlin.com/linux/v5.3.11/source/fs/exec.c#L451
+
+ // Get our current limit, and set things up so we restore the limit.
+ rlimit rl;
+ ASSERT_EQ(0, getrlimit(RLIMIT_STACK, &rl));
+ uint64_t original_rlim_cur = rl.rlim_cur;
+ if (rl.rlim_cur == RLIM_INFINITY) {
+ rl.rlim_cur = 8 * 1024 * 1024; // Bionic reports unlimited stacks as 8MiB.
+ }
+ auto guard = android::base::make_scope_guard([&rl, original_rlim_cur]() {
+ rl.rlim_cur = original_rlim_cur;
+ ASSERT_EQ(0, setrlimit(RLIMIT_STACK, &rl));
+ });
+
+ // _SC_ARG_MAX should be 1/4 the stack size.
+ EXPECT_EQ(static_cast<long>(rl.rlim_cur / 4), sysconf(_SC_ARG_MAX));
+
+ // If you have a really small stack, the kernel still guarantees "32 pages" (see fs/exec.c).
+ rl.rlim_cur = 1024;
+ rl.rlim_max = RLIM_INFINITY;
+ ASSERT_EQ(0, setrlimit(RLIMIT_STACK, &rl));
+
+ EXPECT_EQ(static_cast<long>(32 * sysconf(_SC_PAGE_SIZE)), sysconf(_SC_ARG_MAX));
+
+ // With a 128-page stack limit, we know exactly what _SC_ARG_MAX should be...
+ rl.rlim_cur = 128 * sysconf(_SC_PAGE_SIZE);
+ rl.rlim_max = RLIM_INFINITY;
+ ASSERT_EQ(0, setrlimit(RLIMIT_STACK, &rl));
+
+ EXPECT_EQ(static_cast<long>((128 * sysconf(_SC_PAGE_SIZE)) / 4), sysconf(_SC_ARG_MAX));
}
TEST(UNISTD_TEST, sysconf_unknown) {