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[libc] Support opaque FILE* on baremetal #168931

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[libc] Support opaque FILE* on baremetal
petrhosek Nov 20, 2025
01cb398
Include missing files
petrhosek Nov 20, 2025
f812a2c
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petrhosek Nov 20, 2025
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6 changes: 4 additions & 2 deletions clang/cmake/caches/Fuchsia-stage2.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -341,7 +341,7 @@ foreach(target armv6m-none-eabi;armv7m-none-eabi;armv7em-none-eabi;armv8m.main-n
foreach(lang C;CXX;ASM)
# TODO: The preprocessor defines workaround various issues in libc and libc++ integration.
# These should be addressed and removed over time.
set(RUNTIMES_${target}_CMAKE_${lang}_local_flags "--target=${target} -Wno-atomic-alignment \"-Dvfprintf(stream, format, vlist)=vprintf(format, vlist)\" \"-Dfprintf(stream, format, ...)=printf(format)\" \"-Dfputs(string, stream)=puts(string)\" -D_LIBCPP_PRINT=1")
set(RUNTIMES_${target}_CMAKE_${lang}_local_flags "--target=${target} -Wno-atomic-alignment")
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@Prabhuk Prabhuk Nov 20, 2025

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You may also want to update libc/cmake/cache files introduced recently. e.g. https://github.com/llvm/llvm-project/blob/main/libc/cmake/caches/armv6m-none-eabi.cmake

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@petrhosek petrhosek Nov 20, 2025

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Those flags are only needed for building for libc++ which we don't do in those cache files, so we can remove those flags separately from this PR (I forgot to catch that in the review).

if(NOT ${target} STREQUAL "aarch64-none-elf")
set(RUNTIMES_${target}_CMAKE_${lang}_local_flags "${RUNTIMES_${target}_CMAKE_${lang}_local_flags} -mthumb")
endif()
Expand Down Expand Up @@ -372,6 +372,7 @@ foreach(target armv6m-none-eabi;armv7m-none-eabi;armv7em-none-eabi;armv8m.main-n
set(RUNTIMES_${target}_LIBCXX_ENABLE_RTTI OFF CACHE BOOL "")
set(RUNTIMES_${target}_LIBCXX_ENABLE_THREADS OFF CACHE BOOL "")
set(RUNTIMES_${target}_LIBCXX_ENABLE_MONOTONIC_CLOCK OFF CACHE BOOL "")
set(RUNTIMES_${target}_LIBCXX_HAS_TERMINAL_AVAILABLE OFF CACHE BOOL "")
set(RUNTIMES_${target}_LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
set(RUNTIMES_${target}_LLVM_INCLUDE_TESTS OFF CACHE BOOL "")
set(RUNTIMES_${target}_LLVM_ENABLE_ASSERTIONS OFF CACHE BOOL "")
Expand Down Expand Up @@ -406,7 +407,7 @@ foreach(target riscv32-unknown-elf)
foreach(lang C;CXX;ASM)
# TODO: The preprocessor defines workaround various issues in libc and libc++ integration.
# These should be addressed and removed over time.
set(RUNTIMES_${target}_CMAKE_${lang}_FLAGS "--target=${target} -march=rv32imafc -mabi=ilp32f -Wno-atomic-alignment \"-Dvfprintf(stream, format, vlist)=vprintf(format, vlist)\" \"-Dfprintf(stream, format, ...)=printf(format)\" \"-Dfputs(string, stream)=puts(string)\" -D_LIBCPP_PRINT=1" CACHE STRING "")
set(RUNTIMES_${target}_CMAKE_${lang}_FLAGS "--target=${target} -march=rv32imafc -mabi=ilp32f -Wno-atomic-alignment" CACHE STRING "")
endforeach()
foreach(type SHARED;MODULE;EXE)
set(RUNTIMES_${target}_CMAKE_${type}_LINKER_FLAGS "-fuse-ld=lld" CACHE STRING "")
Expand All @@ -427,6 +428,7 @@ foreach(target riscv32-unknown-elf)
set(RUNTIMES_${target}_LIBCXX_ENABLE_RTTI OFF CACHE BOOL "")
set(RUNTIMES_${target}_LIBCXX_ENABLE_THREADS OFF CACHE BOOL "")
set(RUNTIMES_${target}_LIBCXX_ENABLE_MONOTONIC_CLOCK OFF CACHE BOOL "")
set(RUNTIMES_${target}_LIBCXX_HAS_TERMINAL_AVAILABLE OFF CACHE BOOL "")
set(RUNTIMES_${target}_LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
set(RUNTIMES_${target}_LLVM_INCLUDE_TESTS OFF CACHE BOOL "")
set(RUNTIMES_${target}_LLVM_ENABLE_ASSERTIONS OFF CACHE BOOL "")
Expand Down
8 changes: 8 additions & 0 deletions libc/config/baremetal/aarch64/entrypoints.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -124,8 +124,15 @@ set(TARGET_LIBC_ENTRYPOINTS

# stdio.h entrypoints
libc.src.stdio.asprintf
libc.src.stdio.feof
libc.src.stdio.ferror
libc.src.stdio.fprintf
libc.src.stdio.fputc
libc.src.stdio.fputs
libc.src.stdio.fwrite
libc.src.stdio.getchar
libc.src.stdio.printf
libc.src.stdio.putc
libc.src.stdio.putchar
libc.src.stdio.puts
libc.src.stdio.remove
Expand All @@ -134,6 +141,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.stdio.sprintf
libc.src.stdio.sscanf
libc.src.stdio.vasprintf
libc.src.stdio.vfprintf
libc.src.stdio.vprintf
libc.src.stdio.vscanf
libc.src.stdio.vsnprintf
Expand Down
8 changes: 8 additions & 0 deletions libc/config/baremetal/arm/entrypoints.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -124,8 +124,15 @@ set(TARGET_LIBC_ENTRYPOINTS

# stdio.h entrypoints
libc.src.stdio.asprintf
libc.src.stdio.feof
libc.src.stdio.ferror
libc.src.stdio.fprintf
libc.src.stdio.fputc
libc.src.stdio.fputs
libc.src.stdio.fwrite
libc.src.stdio.getchar
libc.src.stdio.printf
libc.src.stdio.putc
libc.src.stdio.putchar
libc.src.stdio.puts
libc.src.stdio.remove
Expand All @@ -134,6 +141,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.stdio.sprintf
libc.src.stdio.sscanf
libc.src.stdio.vasprintf
libc.src.stdio.vfprintf
libc.src.stdio.vprintf
libc.src.stdio.vscanf
libc.src.stdio.vsnprintf
Expand Down
8 changes: 8 additions & 0 deletions libc/config/baremetal/riscv/entrypoints.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -124,8 +124,15 @@ set(TARGET_LIBC_ENTRYPOINTS

# stdio.h entrypoints
libc.src.stdio.asprintf
libc.src.stdio.feof
libc.src.stdio.ferror
libc.src.stdio.fprintf
libc.src.stdio.fputc
libc.src.stdio.fputs
libc.src.stdio.fwrite
libc.src.stdio.getchar
libc.src.stdio.printf
libc.src.stdio.putc
libc.src.stdio.putchar
libc.src.stdio.puts
libc.src.stdio.remove
Expand All @@ -134,6 +141,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.stdio.sprintf
libc.src.stdio.sscanf
libc.src.stdio.vasprintf
libc.src.stdio.vfprintf
libc.src.stdio.vprintf
libc.src.stdio.vscanf
libc.src.stdio.vsnprintf
Expand Down
42 changes: 4 additions & 38 deletions libc/src/__support/OSUtil/baremetal/io.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8,49 +8,15 @@

#include "io.h"

#include "hdr/types/FILE.h"
#include "src/__support/CPP/string_view.h"
#include "src/__support/macros/config.h"

namespace LIBC_NAMESPACE_DECL {

// These are intended to be provided by the vendor.
//
// The signature of these types and functions intentionally match `fopencookie`
// which allows the following:
//
// ```
// struct __llvm_libc_stdio_cookie { ... };
// ...
// struct __llvm_libc_stdio_cookie __llvm_libc_stdin_cookie;
// cookie_io_functions_t stdin_func = { .read = __llvm_libc_stdio_read };
// FILE *stdin = fopencookie(&__llvm_libc_stdin_cookie, "r", stdin_func);
// ...
// struct __llvm_libc_stdio_cookie __llvm_libc_stdout_cookie;
// cookie_io_functions_t stdout_func = { .write = __llvm_libc_stdio_write };
// FILE *stdout = fopencookie(&__llvm_libc_stdout_cookie, "w", stdout_func);
// ...
// struct __llvm_libc_stdio_cookie __llvm_libc_stderr_cookie;
// cookie_io_functions_t stderr_func = { .write = __llvm_libc_stdio_write };
// FILE *stderr = fopencookie(&__llvm_libc_stderr_cookie, "w", stderr_func);
// ```
//
// At the same time, implementation of functions like `printf` and `scanf` can
// use `__llvm_libc_stdio_read` and `__llvm_libc_stdio_write` directly to avoid
// the extra indirection.
//
// All three symbols `__llvm_libc_stdin_cookie`, `__llvm_libc_stdout_cookie`,
// and `__llvm_libc_stderr_cookie` must be provided, even if they don't point
// at anything.

struct __llvm_libc_stdio_cookie;

extern "C" struct __llvm_libc_stdio_cookie __llvm_libc_stdin_cookie;
extern "C" struct __llvm_libc_stdio_cookie __llvm_libc_stdout_cookie;
extern "C" struct __llvm_libc_stdio_cookie __llvm_libc_stderr_cookie;

extern "C" ssize_t __llvm_libc_stdio_read(void *cookie, char *buf, size_t size);
extern "C" ssize_t __llvm_libc_stdio_write(void *cookie, const char *buf,
size_t size);
extern "C" FILE *stdin = reinterpret_cast<FILE *>(&__llvm_libc_stdin_cookie);
extern "C" FILE *stdout = reinterpret_cast<FILE *>(&__llvm_libc_stdout_cookie);
extern "C" FILE *stderr = reinterpret_cast<FILE *>(&__llvm_libc_stderr_cookie);

ssize_t read_from_stdin(char *buf, size_t size) {
return __llvm_libc_stdio_read(static_cast<void *>(&__llvm_libc_stdin_cookie),
Expand Down
39 changes: 39 additions & 0 deletions libc/src/__support/OSUtil/baremetal/io.h
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,45 @@

namespace LIBC_NAMESPACE_DECL {

// These are intended to be provided by the vendor.
//
// The signature of these types and functions intentionally match `fopencookie`
// which allows the following:
//
// ```
// struct __llvm_libc_stdio_cookie { ... };
// ...
// struct __llvm_libc_stdio_cookie __llvm_libc_stdin_cookie;
// cookie_io_functions_t stdin_func = { .read = __llvm_libc_stdio_read };
// FILE *stdin = fopencookie(&__llvm_libc_stdin_cookie, "r", stdin_func);
// ...
// struct __llvm_libc_stdio_cookie __llvm_libc_stdout_cookie;
// cookie_io_functions_t stdout_func = { .write = __llvm_libc_stdio_write };
// FILE *stdout = fopencookie(&__llvm_libc_stdout_cookie, "w", stdout_func);
// ...
// struct __llvm_libc_stdio_cookie __llvm_libc_stderr_cookie;
// cookie_io_functions_t stderr_func = { .write = __llvm_libc_stdio_write };
// FILE *stderr = fopencookie(&__llvm_libc_stderr_cookie, "w", stderr_func);
// ```
//
// At the same time, implementation of functions like `printf` and `scanf` can
// use `__llvm_libc_stdio_read` and `__llvm_libc_stdio_write` directly to avoid
// the extra indirection.
//
// All three symbols `__llvm_libc_stdin_cookie`, `__llvm_libc_stdout_cookie`,
// and `__llvm_libc_stderr_cookie` must be provided, even if they don't point
// at anything.

struct __llvm_libc_stdio_cookie;

extern "C" struct __llvm_libc_stdio_cookie __llvm_libc_stdin_cookie;
extern "C" struct __llvm_libc_stdio_cookie __llvm_libc_stdout_cookie;
extern "C" struct __llvm_libc_stdio_cookie __llvm_libc_stderr_cookie;

extern "C" ssize_t __llvm_libc_stdio_read(void *cookie, char *buf, size_t size);
extern "C" ssize_t __llvm_libc_stdio_write(void *cookie, const char *buf,
size_t size);

ssize_t read_from_stdin(char *buf, size_t size);
void write_to_stderr(cpp::string_view msg);
void write_to_stdout(cpp::string_view msg);
Expand Down
151 changes: 133 additions & 18 deletions libc/src/stdio/baremetal/CMakeLists.txt
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Original file line number Diff line number Diff line change
@@ -1,3 +1,111 @@
add_header_library(
fputc_internal
HDRS
fputc_internal.h
DEPENDS
libc.hdr.types.FILE
libc.src.__support.CPP.string_view
libc.src.__support.OSUtil.osutil
)

add_header_library(
fputs_internal
HDRS
fputs_internal.h
DEPENDS
libc.hdr.types.FILE
libc.src.__support.CPP.string_view
libc.src.__support.OSUtil.osutil
)

add_header_library(
fwrite_internal
HDRS
fwrite_internal.h
DEPENDS
libc.hdr.types.FILE
libc.src.__support.OSUtil.osutil
)

add_header_library(
vfprintf_internal
HDRS
vfprintf_internal.h
DEPENDS
libc.hdr.types.FILE
libc.hdr.stdio_macros
libc.src.__support.arg_list
libc.src.__support.CPP.limits
libc.src.__support.CPP.string_view
libc.src.__support.libc_errno
libc.src.__support.OSUtil.osutil
libc.src.stdio.printf_core.printf_main
libc.src.stdio.printf_core.writer
libc.src.stdio.printf_core.error_mapper
libc.src.stdio.printf_core.core_structs
)

add_entrypoint_object(
feof
SRCS
feof.cpp
HDRS
../feof.h
DEPENDS
libc.hdr.types.FILE
)

add_entrypoint_object(
ferror
SRCS
ferror.cpp
HDRS
../ferror.h
DEPENDS
libc.hdr.types.FILE
)

add_entrypoint_object(
fprintf
SRCS
fprintf.cpp
HDRS
../fprintf.h
DEPENDS
.vfprintf_internal
libc.src.__support.arg_list
)

add_entrypoint_object(
fputc
SRCS
fputc.cpp
HDRS
../fputc.h
DEPENDS
.fputc_internal
)

add_entrypoint_object(
fputs
SRCS
fputs.cpp
HDRS
../fputc.h
DEPENDS
.fputs_internal
)

add_entrypoint_object(
fwrite
SRCS
fwrite.cpp
HDRS
../fwrite.h
DEPENDS
.fwrite_internal
)

add_entrypoint_object(
getchar
SRCS
Expand Down Expand Up @@ -27,14 +135,8 @@ add_entrypoint_object(
HDRS
../printf.h
DEPENDS
libc.src.stdio.printf_core.printf_main
libc.src.stdio.printf_core.writer
libc.src.stdio.printf_core.error_mapper
libc.src.stdio.printf_core.core_structs
.vfprintf_internal
libc.src.__support.arg_list
libc.src.__support.OSUtil.osutil
libc.src.__support.libc_errno
libc.src.__support.CPP.limits
)

add_entrypoint_object(
Expand All @@ -44,8 +146,17 @@ add_entrypoint_object(
HDRS
../putchar.h
DEPENDS
libc.src.__support.OSUtil.osutil
libc.src.__support.CPP.string_view
.fputc_internal
)

add_entrypoint_object(
putc
SRCS
putc.cpp
HDRS
../putc.h
DEPENDS
.fputc_internal
)

add_entrypoint_object(
Expand All @@ -55,8 +166,7 @@ add_entrypoint_object(
HDRS
../puts.h
DEPENDS
libc.src.__support.OSUtil.osutil
libc.src.__support.CPP.string_view
.fputs_internal
)

add_header_library(
Expand All @@ -82,21 +192,26 @@ add_entrypoint_object(
libc.src.__support.OSUtil.osutil
)

add_entrypoint_object(
vfprintf
SRCS
vfprintf.cpp
HDRS
../vfprintf.h
DEPENDS
.vfprintf_internal
libc.src.__support.arg_list
)

add_entrypoint_object(
vprintf
SRCS
vprintf.cpp
HDRS
../vprintf.h
DEPENDS
libc.src.stdio.printf_core.printf_main
libc.src.stdio.printf_core.writer
libc.src.stdio.printf_core.error_mapper
libc.src.stdio.printf_core.core_structs
.vfprintf_internal
libc.src.__support.arg_list
libc.src.__support.OSUtil.osutil
libc.src.__support.libc_errno
libc.src.__support.CPP.limits
)

add_entrypoint_object(
Expand Down
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