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Support older linux systems #545

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merged 4 commits into from
Jun 17, 2022
Merged

Support older linux systems #545

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0bcb69b
Fix pal_linux.h for older linux systems
mfelsche Jun 16, 2022
977cb25
Check for linux/random.h in CMake
mfelsche Jun 16, 2022
8c92bea
Use CMake module CheckIncludeFilesCXX
mfelsche Jun 16, 2022
1795c1b
Move madvise flag ifdefs into constexpr for cleaner code
mfelsche Jun 16, 2022
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10 changes: 10 additions & 0 deletions CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ endif()

include(CheckCXXCompilerFlag)
include(CheckCXXSourceCompiles)
include(CheckIncludeFileCXX)
include(CMakeDependentOption)

option(SNMALLOC_HEADER_ONLY_LIBRARY "Use snmalloc has a header-only library" OFF)
Expand Down Expand Up @@ -105,6 +106,14 @@ int main() {
return res;
}
" SNMALLOC_PLATFORM_HAS_GETENTROPY)

# check if linux/random.h is available
# older libcs might not have sys/random.h
# but some might provide the necessary flags via linux/random.h
# the __has_include macro isn't working properly on all platforms for that header
# this is why we check its existence here
CHECK_INCLUDE_FILE_CXX(linux/random.h SNMALLOC_HAS_LINUX_RANDOM_H)

# Provide as function so other projects can reuse
# FIXME: This modifies some variables that may or may not be the ones that
# provide flags and so is broken by design. It should be removed once Verona
Expand Down Expand Up @@ -203,6 +212,7 @@ add_as_define(SNMALLOC_QEMU_WORKAROUND)
add_as_define(SNMALLOC_TRACING)
add_as_define(SNMALLOC_CI_BUILD)
add_as_define(SNMALLOC_PLATFORM_HAS_GETENTROPY)
add_as_define(SNMALLOC_HAS_LINUX_RANDOM_H)
if (SNMALLOC_NO_REALLOCARRAY)
add_as_define(SNMALLOC_NO_REALLOCARRAY)
endif()
Expand Down
20 changes: 19 additions & 1 deletion src/snmalloc/pal/pal_linux.h
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,11 @@
# include <sys/mman.h>
# include <sys/prctl.h>
# include <syscall.h>
// __has_include does not reliably determine if we actually have linux/random.h
// available
# if defined(SNMALLOC_HAS_LINUX_RANDOM_H)
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What's going on with __has_include?

It might also be worth a comment here to point out that below we check for SYS_getrandom, which won't be defined if this file isn't included?

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I honestly cannot tell you what is going on with __has_include other than with gcc 9.3 is wasn't picking up the following:

#if __has_include(<linux/random.h>)
#   include <linux/random.h>
#endif

I honestly have no idea why.

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SYS_getrandom seems to come from <syscall.h>

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But overall if both sys/random.h and linux/random.h aren't available, the build will fail.

# include <linux/random.h>
# endif

extern "C" int puts(const char* str);

Expand Down Expand Up @@ -35,6 +40,19 @@ namespace snmalloc
*/
static constexpr int default_mmap_flags = MAP_NORESERVE;

/**
* MADV_FREE is only available since Linux 4.5.
*
* Fallback to MADV_DONTNEED on older kernels
*/
static constexpr int madvise_free_flags =
# ifdef SNMALLOC_HAS_LINUX_RANDOM_H
MADV_FREE
# else
MADV_DONTNEED
# endif
;

static void* reserve(size_t size) noexcept
{
void* p = PALPOSIX<PALLinux>::reserve(size);
Expand Down Expand Up @@ -108,7 +126,7 @@ namespace snmalloc
memset(p, 0x5a, size);

madvise(p, size, MADV_DONTDUMP);
madvise(p, size, MADV_FREE);
madvise(p, size, madvise_free_flags);

if constexpr (PalEnforceAccess)
{
Expand Down