[libc] Add stub for confstr - #218789
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POSIX defines confstr as returning strings for various macros (see: https://pubs.opengroup.org/onlinepubs/9799919799/functions/confstr.html) This PR adds an implementation as experimental that always returns that there's no valid string.
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@llvm/pr-subscribers-libc Author: Michael Jones (michaelrj-google) ChangesPOSIX defines confstr as returning strings for various macros (see: Assisted-by: Automated tooling, human reviewed. Full diff: https://github.com/llvm/llvm-project/pull/218789.diff 10 Files Affected:
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index dfba85299c4da..8008a7776005e 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -1373,6 +1373,11 @@ if(LLVM_LIBC_FULL_BUILD)
endif()
if(LLVM_LIBC_ENABLE_EXPERIMENTAL_ENTRYPOINTS)
+ list(APPEND TARGET_LIBC_ENTRYPOINTS
+ # unistd.h entrypoints
+ libc.src.unistd.confstr
+ )
+
if(LLVM_LIBC_FULL_BUILD)
list(APPEND TARGET_LIBC_ENTRYPOINTS
# net/if.h entrypoints
diff --git a/libc/config/linux/arm/entrypoints.txt b/libc/config/linux/arm/entrypoints.txt
index 1f8c64bcae127..0c7d4085534f3 100644
--- a/libc/config/linux/arm/entrypoints.txt
+++ b/libc/config/linux/arm/entrypoints.txt
@@ -661,6 +661,11 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
)
if(LLVM_LIBC_ENABLE_EXPERIMENTAL_ENTRYPOINTS)
+ list(APPEND TARGET_LIBC_ENTRYPOINTS
+ # unistd.h entrypoints
+ libc.src.unistd.confstr
+ )
+
if(LLVM_LIBC_FULL_BUILD)
list(APPEND TARGET_LIBC_ENTRYPOINTS
# regex.h entrypoints
diff --git a/libc/config/linux/riscv/entrypoints.txt b/libc/config/linux/riscv/entrypoints.txt
index 507670684930c..c049c280b13ac 100644
--- a/libc/config/linux/riscv/entrypoints.txt
+++ b/libc/config/linux/riscv/entrypoints.txt
@@ -1591,6 +1591,11 @@ if(LLVM_LIBC_FULL_BUILD)
endif()
if(LLVM_LIBC_ENABLE_EXPERIMENTAL_ENTRYPOINTS)
+ list(APPEND TARGET_LIBC_ENTRYPOINTS
+ # unistd.h entrypoints
+ libc.src.unistd.confstr
+ )
+
if(LLVM_LIBC_FULL_BUILD)
list(APPEND TARGET_LIBC_ENTRYPOINTS
# net/if.h entrypoints
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 7420a4db3330c..1b6c678a5dc1c 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -1604,6 +1604,11 @@ if(LLVM_LIBC_FULL_BUILD)
endif()
if(LLVM_LIBC_ENABLE_EXPERIMENTAL_ENTRYPOINTS)
+ list(APPEND TARGET_LIBC_ENTRYPOINTS
+ # unistd.h entrypoints
+ libc.src.unistd.confstr
+ )
+
if(LLVM_LIBC_FULL_BUILD)
list(APPEND TARGET_LIBC_ENTRYPOINTS
# net/if.h entrypoints
diff --git a/libc/include/unistd.yaml b/libc/include/unistd.yaml
index 0d5b5e71cf7f3..d6c0235dd830f 100644
--- a/libc/include/unistd.yaml
+++ b/libc/include/unistd.yaml
@@ -103,6 +103,14 @@ functions:
- type: const char *
- type: uid_t
- type: gid_t
+ - name: confstr
+ standards:
+ - posix
+ return_type: size_t
+ arguments:
+ - type: int
+ - type: char *
+ - type: size_t
- name: close
standards:
- posix
diff --git a/libc/src/unistd/CMakeLists.txt b/libc/src/unistd/CMakeLists.txt
index c10ea20681059..6109981b032d2 100644
--- a/libc/src/unistd/CMakeLists.txt
+++ b/libc/src/unistd/CMakeLists.txt
@@ -47,6 +47,19 @@ add_entrypoint_object(
.${LIBC_TARGET_OS}.chown
)
+add_entrypoint_object(
+ confstr
+ SRCS
+ confstr.cpp
+ HDRS
+ confstr.h
+ DEPENDS
+ libc.hdr.types.size_t
+ libc.hdr.unistd_macros
+ libc.src.__support.common
+ libc.src.__support.macros.config
+)
+
add_entrypoint_object(
close
ALIAS
diff --git a/libc/src/unistd/confstr.cpp b/libc/src/unistd/confstr.cpp
new file mode 100644
index 0000000000000..3ea3a275928fb
--- /dev/null
+++ b/libc/src/unistd/confstr.cpp
@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Implementation of confstr
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/confstr.h"
+
+#include "hdr/types/size_t.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(size_t, confstr, (int, char *, size_t)) { return 0; }
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/unistd/confstr.h b/libc/src/unistd/confstr.h
new file mode 100644
index 0000000000000..1792942e6c101
--- /dev/null
+++ b/libc/src/unistd/confstr.h
@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Implementation header for confstr
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_UNISTD_CONFSTR_H
+#define LLVM_LIBC_SRC_UNISTD_CONFSTR_H
+
+#include "hdr/types/size_t.h"
+#include "hdr/unistd_macros.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+size_t confstr(int name, char *buf, size_t len);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_UNISTD_CONFSTR_H
diff --git a/libc/test/src/unistd/CMakeLists.txt b/libc/test/src/unistd/CMakeLists.txt
index a220509308bd4..016752bb16289 100644
--- a/libc/test/src/unistd/CMakeLists.txt
+++ b/libc/test/src/unistd/CMakeLists.txt
@@ -641,6 +641,17 @@ add_libc_test(
)
+add_libc_test(
+ confstr_test
+ SUITE
+ libc_unistd_unittests
+ SRCS
+ confstr_test.cpp
+ DEPENDS
+ libc.hdr.types.size_t
+ libc.src.unistd.confstr
+)
+
add_libc_test(
sysconf_test
SUITE
diff --git a/libc/test/src/unistd/confstr_test.cpp b/libc/test/src/unistd/confstr_test.cpp
new file mode 100644
index 0000000000000..28da2bc521460
--- /dev/null
+++ b/libc/test/src/unistd/confstr_test.cpp
@@ -0,0 +1,34 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Unittests for confstr
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/confstr.h"
+
+#include "hdr/types/size_t.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcConfStrTest, Basic) {
+ char buf[64] = "initial";
+ size_t ret = LIBC_NAMESPACE::confstr(0, buf, sizeof(buf));
+ EXPECT_EQ(ret, size_t(0));
+}
+
+TEST(LlvmLibcConfStrTest, NullBufZeroLen) {
+ size_t ret = LIBC_NAMESPACE::confstr(0, nullptr, 0);
+ EXPECT_EQ(ret, size_t(0));
+}
+
+TEST(LlvmLibcConfStrTest, NonExistentConfig) {
+ char buf[64];
+ size_t ret = LIBC_NAMESPACE::confstr(-1, buf, sizeof(buf));
+ EXPECT_EQ(ret, size_t(0));
+}
|
vonosmas
reviewed
Aug 25, 2026
| endif() | ||
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|
||
| if(LLVM_LIBC_ENABLE_EXPERIMENTAL_ENTRYPOINTS) | ||
| list(APPEND TARGET_LIBC_ENTRYPOINTS |
Contributor
There was a problem hiding this comment.
Eh, I don't see how it's fundamentally different from, say, sysconf() where we only support a handful of values for now instead of full slate of arguments. As such, I don't think listing it in "experimental" would be helpful. The function logic is behaving as expected, it's just that we don't provide configuration strings yet. Deferring to you though.
Member
Author
There was a problem hiding this comment.
I'm not feeling super picky. It's technically an invalid implementation since POSIX does specify a bunch of macros but I'm not worried about it.
vonosmas
approved these changes
Aug 25, 2026
| HDRS | ||
| confstr.h | ||
| DEPENDS | ||
| libc.hdr.errno_macros |
Contributor
There was a problem hiding this comment.
I think you need libc.src.errno.errno dependency here to actually set it.
| #define LLVM_LIBC_SRC_UNISTD_CONFSTR_H | ||
|
|
||
| #include "hdr/types/size_t.h" | ||
| #include "hdr/unistd_macros.h" |
Contributor
There was a problem hiding this comment.
Should this be included in .cpp file instead?
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| using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Fails; | ||
|
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| TEST(LlvmLibcConfStrTest, InvalidName) { |
Contributor
There was a problem hiding this comment.
Nit: also use ErrnoCheckingTest to clear out errno before the test / ensure it's validated after the test.
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POSIX defines confstr as returning strings for various macros (see:
https://pubs.opengroup.org/onlinepubs/9799919799/functions/confstr.html)
This PR adds an implementation as experimental that always returns that
there's no valid string.
Assisted-by: Automated tooling, human reviewed.