[clang] [libc] Attempt to enable missing string functions for offloading (PR #67869)
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Fri Sep 29 17:03:56 PDT 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
<details>
<summary>Changes</summary>
Summary:
We previously had to disable these string functions because they were
not compatible with the definitions coming from the GNU / host
environment. The GPU, when exporting its declarations, has a very
difficult requirement that it be compatible with the host environment as
both sides of the compilation need to agree on definitions and what's
present.
For `string.h`, some functions have different defintions for C and C++.
GNU would optionally provide the C++ definitions directly in the
`string.h` file. This patch attempts to hack around this by tricking the
GNU headers into thinking that the `clang` used it too old to support
their special definition handling. The blast radius from this hack
should be somewhat minimal, only changing C++ behaviour for a few
functions. The only noticable change is that we lose const error
checking for a small handful of functions if the user includes
`string.h` directly in C++ mode instead of <cstring>.
---
Full diff: https://github.com/llvm/llvm-project/pull/67869.diff
3 Files Affected:
- (modified) clang/lib/Headers/llvm_libc_wrappers/string.h (+24-3)
- (modified) libc/config/gpu/entrypoints.txt (+16)
- (modified) libc/docs/gpu/support.rst (+19-8)
``````````diff
diff --git a/clang/lib/Headers/llvm_libc_wrappers/string.h b/clang/lib/Headers/llvm_libc_wrappers/string.h
index 027c415c1d0f8f3..0fa6d81fda36b61 100644
--- a/clang/lib/Headers/llvm_libc_wrappers/string.h
+++ b/clang/lib/Headers/llvm_libc_wrappers/string.h
@@ -13,11 +13,32 @@
#error "This file is for GPU offloading compilation only"
#endif
-// FIXME: The GNU headers provide C++ standard compliant headers when in C++
-// mode and the LLVM libc does not. We cannot enable memchr, strchr, strchrnul,
-// strpbrk, strrchr, strstr, or strcasestr until this is addressed.
+// The GNU headers provide C++ standard compliant headers when in C++ mode and
+// the LLVM libc does not. We need to perform a pretty nasty hack to trick the
+// GNU headers into emitting the C compatible definitions so we can use them.
+#if defined(__cplusplus) && defined(__GLIBC__)
+
+// We need to make sure that the GNU C library has done its setup before we mess
+// with the expected macro values.
+#if !defined(__GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION) && \
+ __has_include(<bits/libc-header-start.h>)
+#define __GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION
+#include <bits/libc-header-start.h>
+#endif
+
+// Trick the GNU headers into thinking that this clang is too old for the C++
+// definitions.
+#pragma push_macro("__clang_major__")
+#define __clang_major__ 3
+#endif
+
#include_next <string.h>
+// Resore the original macros if they were changed.
+#if defined(__cplusplus) && defined(__GLIBC__)
+#pragma pop_macro("__clang_major__")
+#endif
+
#if __has_include(<llvm-libc-decls/string.h>)
#if defined(__HIP__) || defined(__CUDA__)
diff --git a/libc/config/gpu/entrypoints.txt b/libc/config/gpu/entrypoints.txt
index ad68216a76b9429..dcaca15b500cbe9 100644
--- a/libc/config/gpu/entrypoints.txt
+++ b/libc/config/gpu/entrypoints.txt
@@ -22,21 +22,31 @@ set(TARGET_LIBC_ENTRYPOINTS
# string.h entrypoints
libc.src.string.bcmp
+ libc.src.string.bcopy
libc.src.string.bzero
+ libc.src.string.index
libc.src.string.memccpy
+ libc.src.string.memchr
libc.src.string.memcmp
libc.src.string.memcpy
libc.src.string.memmem
libc.src.string.memmove
libc.src.string.mempcpy
+ libc.src.string.memrchr
libc.src.string.memset
+ libc.src.string.rindex
libc.src.string.stpcpy
libc.src.string.stpncpy
libc.src.string.strcasecmp
+ libc.src.string.strcasestr
libc.src.string.strcat
+ libc.src.string.strchr
+ libc.src.string.strchrnul
libc.src.string.strcmp
+ libc.src.string.strcoll
libc.src.string.strcpy
libc.src.string.strcspn
+ libc.src.string.strdup
libc.src.string.strlcat
libc.src.string.strlcpy
libc.src.string.strlen
@@ -44,10 +54,16 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.string.strncat
libc.src.string.strncmp
libc.src.string.strncpy
+ libc.src.string.strndup
libc.src.string.strnlen
+ libc.src.string.strpbrk
+ libc.src.string.strrchr
+ libc.src.string.strsep
libc.src.string.strspn
+ libc.src.string.strstr
libc.src.string.strtok
libc.src.string.strtok_r
+ libc.src.string.strxfrm
# stdlib.h entrypoints
libc.src.stdlib.abs
diff --git a/libc/docs/gpu/support.rst b/libc/docs/gpu/support.rst
index fd27273ed562e49..beca7b587a05215 100644
--- a/libc/docs/gpu/support.rst
+++ b/libc/docs/gpu/support.rst
@@ -45,37 +45,48 @@ string.h
Function Name Available RPC Required
============= ========= ============
bcmp |check|
+bcopy |check|
bzero |check|
+index |check|
memccpy |check|
-memchr
+memchr |check|
memcmp |check|
memcpy |check|
+memmem |check|
memmove |check|
mempcpy |check|
-memrchr
+memrchr |check|
memset |check|
+rindex |check|
stpcpy |check|
stpncpy |check|
+strcasecmp |check|
+strcasestr |check|
strcat |check|
-strchr
+strchr |check|
+strchrnul |check|
strcmp |check|
+strcoll |check|
strcpy |check|
strcspn |check|
+strdup |check|
strlcat |check|
strlcpy |check|
strlen |check|
+strncasecmp |check|
strncat |check|
strncmp |check|
strncpy |check|
+strndup |check|
strnlen |check|
-strpbrk
-strrchr
+strpbrk |check|
+strrchr |check|
+strsep |check|
strspn |check|
-strstr
+strstr |check|
strtok |check|
strtok_r |check|
-strdup
-strndup
+strxfrm |check|
============= ========= ============
stdlib.h
``````````
</details>
https://github.com/llvm/llvm-project/pull/67869
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