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Obtain a file lock with flock() while creating a separate debug file
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315dfd3244
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@ -795,6 +795,14 @@ private:
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int perm;
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};
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template <typename Context>
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class LockingOutputFile : public OutputFile<Context> {
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public:
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LockingOutputFile(Context &ctx, std::string path, int perm);
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void resize(Context &ctx, i64 filesize);
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void close(Context &ctx) override;
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};
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//
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// hyperloglog.cc
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//
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@ -2,6 +2,7 @@
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#include <fcntl.h>
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#include <filesystem>
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#include <sys/file.h>
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#include <sys/mman.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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@ -143,4 +144,52 @@ OutputFile<Context>::open(Context &ctx, std::string path, i64 filesize, int perm
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return std::unique_ptr<OutputFile>(file);
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}
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// LockingOutputFile is similar to MemoryMappedOutputFile, but it doesn't
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// rename output files and instead acquires file lock using flock().
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template <typename Context>
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LockingOutputFile<Context>::LockingOutputFile(Context &ctx, std::string path,
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int perm)
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: OutputFile<Context>(path, 0, true) {
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this->fd = ::open(path.c_str(), O_RDWR | O_CREAT, perm);
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if (this->fd == -1)
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Fatal(ctx) << "cannot open " << path << ": " << errno_string();
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flock(this->fd, LOCK_EX);
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// We may be overwriting to an existing debug info file. We want to
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// make the file unusable so that gdb won't use it by accident until
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// it's ready.
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u8 buf[256] = {};
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(void)!!write(this->fd, buf, sizeof(buf));
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}
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template <typename Context>
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void LockingOutputFile<Context>::resize(Context &ctx, i64 filesize) {
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if (ftruncate(this->fd, filesize) == -1)
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Fatal(ctx) << "ftruncate failed: " << errno_string();
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this->buf = (u8 *)mmap(nullptr, filesize, PROT_READ | PROT_WRITE,
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MAP_SHARED, this->fd, 0);
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if (this->buf == MAP_FAILED)
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Fatal(ctx) << this->path << ": mmap failed: " << errno_string();
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this->filesize = filesize;
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mold::output_buffer_start = this->buf;
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mold::output_buffer_end = this->buf + filesize;
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}
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template <typename Context>
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void LockingOutputFile<Context>::close(Context &ctx) {
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if (!this->is_unmapped)
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munmap(this->buf, this->filesize);
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if (!this->buf2.empty()) {
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FILE *out = fdopen(this->fd, "w");
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fseek(out, 0, SEEK_END);
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fwrite(&this->buf2[0], this->buf2.size(), 1, out);
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fclose(out);
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}
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::close(this->fd);
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}
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} // namespace mold
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@ -97,4 +97,17 @@ OutputFile<Context>::open(Context &ctx, std::string path, i64 filesize, int perm
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return std::unique_ptr<OutputFile<Context>>(file);
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}
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template <typename Context>
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LockingOutputFile<Context>::LockingOutputFile(Context &ctx, std::string path,
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int perm)
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: OutputFile<Context>(path, 0, true) {
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Fatal(ctx) << "LockingOutputFile is not supported on Windows";
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}
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template <typename Context>
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void LockingOutputFile<Context>::resize(Context &ctx, i64 filesize) {}
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template <typename Context>
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void LockingOutputFile<Context>::close(Context &ctx) {}
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} // namespace mold
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@ -1,5 +1,6 @@
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#include "mold.h"
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#include "blake3.h"
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#include "../common/output-file.h"
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#include <fstream>
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#include <functional>
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@ -3056,6 +3057,10 @@ template <typename E>
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void write_separate_debug_file(Context<E> &ctx) {
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Timer t(ctx, "write_separate_debug_file");
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// Open an output file early
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LockingOutputFile<Context<E>> *file =
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new LockingOutputFile<Context<E>>(ctx, ctx.arg.separate_debug_file, 0666);
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// We want to write to the debug info file in background so that the
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// user doesn't have to wait for it to complete.
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if (ctx.arg.detach)
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@ -3087,11 +3092,9 @@ void write_separate_debug_file(Context<E> &ctx) {
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// Write to the debug info file as if it were a regular output file.
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compute_section_headers(ctx);
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i64 filesize = set_osec_offsets(ctx);
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file->resize(ctx, set_osec_offsets(ctx));
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ctx.output_file =
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OutputFile<Context<E>>::open(ctx, ctx.arg.separate_debug_file,
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filesize, 0666);
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ctx.output_file.reset(file);
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ctx.buf = ctx.output_file->buf;
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copy_chunks(ctx);
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@ -3102,7 +3105,7 @@ void write_separate_debug_file(Context<E> &ctx) {
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// Reverse-compute a CRC32 value so that the CRC32 checksum embedded to
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// the .gnu_debuglink section in the main executable matches with the
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// debug info file's CRC32 checksum.
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u32 crc = compute_crc32(0, ctx.buf, filesize);
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u32 crc = compute_crc32(0, ctx.buf, ctx.output_file->filesize);
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std::vector<u8> &buf2 = ctx.output_file->buf2;
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if (!buf2.empty())
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@ -16,11 +16,12 @@ $CC -c -o $t/a.o $t/a.c -g
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$CC -B. -o $t/exe1 $t/a.o -Wl,--separate-debug-file
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readelf -SW $t/exe1 | grep -Fq .gnu_debuglink
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flock $t/exe1 true
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gdb $t/exe1 -ex 'list main' -ex 'quit' | grep -Fq printf
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$CC -c -o $t/a.o $t/a.c -g
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$CC -B. -o $t/exe2 $t/a.o -Wl,--separate-debug-file -Wl,--no-build-id
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readelf -SW $t/exe2 | grep -Fq .gnu_debuglink
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sleep 1
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gdb $t/exe1 -ex 'list main' -ex 'quit' | grep -Fq printf
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flock $t/exe2 true
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gdb $t/exe2 -ex 'list main' -ex 'quit' | grep -Fq printf
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