[libc] fix sysconf test for rv32 #162685
[libc] fix sysconf test for rv32 #162685
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@llvm/pr-subscribers-backend-risc-v @llvm/pr-subscribers-libc Author: Schrodinger ZHU Yifan (SchrodingerZhu) ChangesOn 32-bit architectures, MMAP may return userspace virtual address with high bit set. This patch copy the err detection logic from existing mmap function implementation. Full diff: https://github.com/llvm/llvm-project/pull/162685.diff 1 Files Affected:
diff --git a/libc/src/__support/OSUtil/linux/auxv.h b/libc/src/__support/OSUtil/linux/auxv.h
index 894868ae5824d..cca0f358e2366 100644
--- a/libc/src/__support/OSUtil/linux/auxv.h
+++ b/libc/src/__support/OSUtil/linux/auxv.h
@@ -16,6 +16,7 @@
#include <linux/auxvec.h> // For AT_ macros
#include <linux/mman.h> // For mmap flags
+#include <linux/param.h> // For EXEC_PAGESIZE
#include <linux/prctl.h> // For prctl
#include <sys/syscall.h> // For syscall numbers
@@ -90,7 +91,7 @@ LIBC_INLINE void Vector::fallback_initialize_unsync() {
PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
// We do not proceed if mmap fails.
- if (mmap_ret <= 0)
+ if (mmap_ret <= 0 && mmap_ret > -EXEC_PAGESIZE)
return;
// Initialize the auxv array with AT_NULL entries.
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| MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); | ||
| // We do not proceed if mmap fails. | ||
| if (mmap_ret <= 0) | ||
| if (mmap_ret <= 0 && mmap_ret > -EXEC_PAGESIZE) |
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I think we should restrict this extra condition to RV32 only, and add comments to explain the reason.
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So the original mmap.cpp always have this check logic.
However, I read the comment again and the argument looks suspicious. EXEC_PAGESIZE is not always the page size in general.
Inside linux kernel, the logic is defined in https://elixir.bootlin.com/linux/v6.17.1/source/tools/include/linux/err.h#L33.
I think the checking logic should be provided as a common function and used in both cases.
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Having a common check function and link to the linux kernel would be great.
| template <typename PointerLike> | ||
| LIBC_INLINE constexpr bool is_valid_mmap(PointerLike ptr) { | ||
| long addr = cpp::bit_cast<long>(ptr); | ||
| return __builtin_expect(addr > 0 || addr < -cpp::bit_cast<long>(MAX_ERRNO), |
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Use LIBC_LIKELY from https://github.com/llvm/llvm-project/blob/main/libc/src/__support/macros/optimization.h#L27
and for casting signed / unsigned integers, static_cast should be good enough.
3 participants
Closes #162671
On 32-bit architectures, MMAP may return userspace virtual address with high bit set. This patch copy the err detection logic from existing mmap function implementation.