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https://github.com/rui314/mold.git
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fe209f3f4c
We try to overwrite to an existing output file if exists because writing to a file that is already in buffer cache is much faster than creating a new fresh file and write to it. Previously, mold failed with the "fchmod failed" error if an existing file is writable (so open for read-write succeeds) but owned by someone else (so fchown fails). Now, mold ignore such existing file and create a fresh output file. Fixes https://github.com/rui314/mold/issues/275
143 lines
3.9 KiB
C++
143 lines
3.9 KiB
C++
#include "mold.h"
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#include <fcntl.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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namespace mold::elf {
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inline u32 get_umask() {
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u32 orig_umask = umask(0);
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umask(orig_umask);
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return orig_umask;
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}
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template <typename C>
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static std::pair<i64, char *>
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open_or_create_file(C &ctx, std::string path, i64 filesize, i64 perm) {
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std::string tmpl = filepath(path).parent_path() / ".mold-XXXXXX";
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char *path2 = (char *)save_string(ctx, tmpl).data();
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i64 fd = mkstemp(path2);
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if (fd == -1)
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Fatal(ctx) << "cannot open " << path2 << ": " << errno_string();
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// Reuse an existing file if exists and writable.
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if (rename(path.c_str(), path2) == 0) {
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::close(fd);
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fd = ::open(path2, O_RDWR | O_CREAT, perm);
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if (fd != -1 && !ftruncate(fd, filesize) && !fchmod(fd, perm & ~get_umask()))
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return {fd, path2};
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unlink(path2);
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fd = ::open(path2, O_RDWR | O_CREAT, perm);
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if (fd == -1)
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Fatal(ctx) << "cannot open " << path2 << ": " << errno_string();
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}
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if (ftruncate(fd, filesize))
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Fatal(ctx) << "ftruncate failed: " << errno_string();
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if (fchmod(fd, (perm & ~get_umask())) == -1)
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Fatal(ctx) << "fchmod failed: " << errno_string();
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return {fd, path2};
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}
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template <typename E>
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class MemoryMappedOutputFile : public OutputFile<E> {
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public:
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MemoryMappedOutputFile(Context<E> &ctx, std::string path, i64 filesize, i64 perm)
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: OutputFile<E>(path, filesize, true) {
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i64 fd;
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std::tie(fd, output_tmpfile) = open_or_create_file(ctx, path, filesize, perm);
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this->buf = (u8 *)mmap(nullptr, filesize, PROT_READ | PROT_WRITE,
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MAP_SHARED, fd, 0);
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if (this->buf == MAP_FAILED)
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Fatal(ctx) << path << ": mmap failed: " << errno_string();
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::close(fd);
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}
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void close(Context<E> &ctx) override {
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Timer t(ctx, "close_file");
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if (!this->is_unmapped)
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munmap(this->buf, this->filesize);
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if (rename(output_tmpfile, this->path.c_str()) == -1)
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Fatal(ctx) << this->path << ": rename failed: " << errno_string();
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output_tmpfile = nullptr;
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}
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};
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template <typename E>
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class MallocOutputFile : public OutputFile<E> {
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public:
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MallocOutputFile(Context<E> &ctx, std::string path, i64 filesize, i64 perm)
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: OutputFile<E>(path, filesize, false), perm(perm) {
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this->buf = (u8 *)mmap(NULL, filesize, PROT_READ | PROT_WRITE,
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MAP_SHARED | MAP_ANONYMOUS, -1, 0);
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if (this->buf == MAP_FAILED)
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Fatal(ctx) << "mmap failed: " << errno_string();
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}
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void close(Context<E> &ctx) override {
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Timer t(ctx, "close_file");
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if (this->path == "-") {
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fwrite(this->buf, this->filesize, 1, stdout);
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fclose(stdout);
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return;
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}
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i64 fd = ::open(this->path.c_str(), O_RDWR | O_CREAT, perm);
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if (fd == -1)
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Fatal(ctx) << "cannot open " << this->path << ": " << errno_string();
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FILE *fp = fdopen(fd, "w");
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fwrite(this->buf, this->filesize, 1, fp);
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fclose(fp);
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}
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private:
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i64 perm;
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};
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template <typename E>
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std::unique_ptr<OutputFile<E>>
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OutputFile<E>::open(Context<E> &ctx, std::string path, i64 filesize, i64 perm) {
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Timer t(ctx, "open_file");
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if (path.starts_with('/') && !ctx.arg.chroot.empty())
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path = ctx.arg.chroot + "/" + path_clean(path);
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bool is_special = false;
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if (path == "-") {
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is_special = true;
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} else {
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struct stat st;
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if (stat(path.c_str(), &st) == 0 && (st.st_mode & S_IFMT) != S_IFREG)
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is_special = true;
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}
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std::unique_ptr<OutputFile<E>> file;
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if (is_special)
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file = std::make_unique<MallocOutputFile<E>>(ctx, path, filesize, perm);
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else
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file = std::make_unique<MemoryMappedOutputFile<E>>(ctx, path, filesize, perm);
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if (ctx.arg.filler != -1)
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memset(file->buf, ctx.arg.filler, filesize);
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return file;
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}
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#define INSTANTIATE(E) \
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template class OutputFile<E>;
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INSTANTIATE(X86_64);
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INSTANTIATE(I386);
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INSTANTIATE(ARM64);
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} // namespace mold::elf
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