* Re: I need a new configure toggle to completely remove emergency heap
2022-10-12 14:45 ` unlvsur unlvsur
@ 2022-10-12 22:13 ` Jonathan Wakely
0 siblings, 0 replies; 4+ messages in thread
From: Jonathan Wakely @ 2022-10-12 22:13 UTC (permalink / raw)
To: unlvsur unlvsur; +Cc: unlvsur unlvsur via Libstdc++
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On Wed, 12 Oct 2022 at 15:45, unlvsur unlvsur <unlvsur@live.com> wrote:
>
> But the code is still there. tbh i have patched them myself to remove emergency heap and all its related logic completely for a very long time and i never see any abi issues around it.
>
> The toggle i need should just disable all code around it
So like this untested patch.
We should probably also make __cxa_free_dependent_exception an alias
of __cxa_free_exception to save a few more bytes.
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commit 5c4a63e883efe0e3910a8bb391d3091cb8558d54
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Wed Oct 12 23:04:53 2022
libstdc++: Disable all emergency EH pool code if obj-count == 0
For a zero-sized static pool we can completely elide all code for the EH
pool.
libstdc++-v3/ChangeLog:
* libsupc++/eh_alloc.cc [EMERGENCY_OBJ_COUNT==0]
[!USE_POOL] (__gnu_cxx::__freeres, pool): Do not define.
(__cxxabiv1::__cxa_allocate_exception) [!USE_POOL]: Do not use
pool.
(__cxxabiv1::__cxa_free_exception) [!USE_POOL]: Likewise.
(__cxxabiv1::__cxa_allocate_dependent_exception) [!USE_POOL]:
Likewise.
(__cxxabiv1::__cxa_free_dependent_exception) [!USE_POOL]:
Likewise.
diff --git a/libstdc++-v3/libsupc++/eh_alloc.cc b/libstdc++-v3/libsupc++/eh_alloc.cc
index 81b8a1548c6..adf027a3b64 100644
--- a/libstdc++-v3/libsupc++/eh_alloc.cc
+++ b/libstdc++-v3/libsupc++/eh_alloc.cc
@@ -101,12 +101,15 @@ using namespace __cxxabiv1;
#ifdef _GLIBCXX_EH_POOL_NOBJS
# if _GLIBCXX_EH_POOL_NOBJS > MAX_OBJ_COUNT
# warning "_GLIBCXX_EH_POOL_NOBJS value is too large; ignoring it"
+# elif _GLIBCXX_EH_POOL_NOBJS < 0
+# warning "_GLIBCXX_EH_POOL_NOBJS value is negative; ignoring it"
# else
# undef EMERGENCY_OBJ_COUNT
# define EMERGENCY_OBJ_COUNT _GLIBCXX_EH_POOL_NOBJS
# endif
#endif
+#if EMERGENCY_OBJ_COUNT > 0
namespace __gnu_cxx
{
void __freeres() noexcept;
@@ -374,6 +377,7 @@ namespace __gnu_cxx
#endif
}
}
+#endif // EMERGENCY_OBJ_COUNT > 0
extern "C" void *
__cxxabiv1::__cxa_allocate_exception(std::size_t thrown_size) noexcept
@@ -382,8 +386,10 @@ __cxxabiv1::__cxa_allocate_exception(std::size_t thrown_size) noexcept
void *ret = malloc (thrown_size);
+#if EMERGENCY_OBJ_COUNT > 0
if (!ret)
ret = emergency_pool.allocate (thrown_size);
+#endif
if (!ret)
std::terminate ();
@@ -398,9 +404,11 @@ extern "C" void
__cxxabiv1::__cxa_free_exception(void *vptr) noexcept
{
char *ptr = (char *) vptr - sizeof (__cxa_refcounted_exception);
+#if EMERGENCY_OBJ_COUNT > 0
if (emergency_pool.in_pool (ptr)) [[__unlikely__]]
emergency_pool.free (ptr);
else
+#endif
free (ptr);
}
@@ -410,8 +418,10 @@ __cxxabiv1::__cxa_allocate_dependent_exception() noexcept
{
void *ret = malloc (sizeof (__cxa_dependent_exception));
+#if EMERGENCY_OBJ_COUNT > 0
if (!ret)
ret = emergency_pool.allocate (sizeof (__cxa_dependent_exception));
+#endif
if (!ret)
std::terminate ();
@@ -426,8 +436,10 @@ extern "C" void
__cxxabiv1::__cxa_free_dependent_exception
(__cxa_dependent_exception *vptr) noexcept
{
+#if EMERGENCY_OBJ_COUNT > 0
if (emergency_pool.in_pool (vptr)) [[__unlikely__]]
emergency_pool.free (vptr);
else
+#endif
free (vptr);
}
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