Merge 4011923433 into 18da5b654e

--detach is the default.

.github/dependabot.yml

@@ -0,0 +1,17 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions" # See documentation for possible values
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "daily"
+
+  - package-ecosystem: "github-actions" # See documentation for possible values
+    directory: "/common" # Location of package manifests
+    schedule:
+      interval: "daily"
+    

common/common.h

@@ -905,7 +905,7 @@ void release_global_lock();
 //
 
 u32 compute_crc32(u32 crc, u8 *buf, i64 len);
-std::vector<u8> crc32_solve(i64 datalen, u32 current, u32 want);
+std::vector<u8> crc32_solve(u32 current, u32 desired);
 
 //
 // compress.cc

common/crc32.cc

@@ -1,42 +1,3 @@
-// This file contains a function to "forge" a CRC. That is, given a piece
-// of data and a desired CRC32 value, crc32_solve() returns a binary blob
-// to add to the end of the original data to yield the desired CRC32
-// value. A trailing garbage is ignored for many bianry file formats, so
-// you can create a file with a desired CRC using crc32_solve(). We need
-// it for --separate-debug-info.
-//
-// The code in this file is based on Mark Adler's "spoof" program. You can
-// obtain the original copy of it at the following URL:
-//
-//   https://github.com/madler/spoof/blob/master/spoof.c
-//
-// Below is the original license:
-
-/* spoof.c -- modify a message to have a desired CRC
-
-  Copyright (C) 2012, 2014, 2016, 2018, 2021 Mark Adler
-
-  This software is provided 'as-is', without any express or implied warranty.
-  In no event will the authors be held liable for any damages arising from the
-  use of this software.
-
-  Permission is granted to anyone to use this software for any purpose,
-  including commercial applications, and to alter it and redistribute it
-  freely, subject to the following restrictions:
-
-  1. The origin of this software must not be misrepresented; you must not claim
-     that you wrote the original software. If you use this software in a
-     product, an acknowledgment in the product documentation would be
-     appreciated but is not required.
-  2. Altered source versions must be plainly marked as such, and must not be
-     misrepresented as being the original software.
-  3. This notice may not be removed or altered from any source distribution.
-
-  Mark Adler
-  madler@alumni.caltech.edu
-
- */
-
 #include "common.h"
 
 #include <tbb/parallel_for_each.h>
@@ -44,101 +5,29 @@
 
 namespace mold {
 
-static constexpr i64 deg = 32;
-static constexpr u32 poly = 0xedb88320;
+// This function "forges" a CRC. That is, given the current and a desired
+// CRC32 value, crc32_solve() returns a binary blob to add to the end of
+// the original data to yield the desired CRC. Trailing garbage is ignored
+// by many bianry file formats, so you can create a file with a desired
+// CRC using crc32_solve(). We need it for --separate-debug-file.
+std::vector<u8> crc32_solve(u32 current, u32 desired) {
+  constexpr u32 poly = 0xedb88320;
+  u32 x = ~desired;
 
-using Mat = std::array<u32, deg>;
-
-static constexpr u32 gf2_matrix_times(const Mat &mat, u32 vec) {
-  u32 n = 0;
-  for (i64 i = 0; vec; vec >>= 1, i++)
-    if (vec & 1)
-      n ^= mat[i];
-  return n;
-}
-
-static constexpr Mat gf2_matrix_square(const Mat &mat) {
-  Mat sq;
-  for (i64 i = 0; i < deg; i++)
-    sq[i] = gf2_matrix_times(mat, mat[i]);
-  return sq;
-}
-
-static consteval std::array<Mat, 64> get_crc_zero_powers() {
-  std::array<Mat, 64> p;
-
-  p[1][0] = poly;
-  for (i64 n = 1; n < deg; n++)
-    p[1][n] = 1 << (n - 1);
-
-  p[0] = gf2_matrix_square(p[1]);
-  p[1] = gf2_matrix_square(p[0]);
-  p[0] = gf2_matrix_square(p[1]);
-  p[1] = gf2_matrix_square(p[0]);
-
-  for (i64 i = 2; i < 64; i++)
-    p[i] = gf2_matrix_square(p[i - 1]);
-  return p;
-}
-
-// Efficiently apply len zero bytes to crc, returning the resulting crc.
-static u32 crc_zeros(u32 crc, i64 len) {
-  static constexpr std::array<Mat, 64> power = get_crc_zero_powers();
-
-  // apply len zeros to crc
-  if (crc)
-    for (i64 n = 0; len; len >>= 1, n++)
-      if (len & 1)
-        crc = gf2_matrix_times(power[n], crc);
-  return crc;
-}
-
-// Solve M x = c for x
-static std::vector<bool> gf2_matrix_solve(std::vector<u32> M, u32 c) {
-  i64 cols = M.size();
-  i64 rows = deg;
-
-  // create adjoining identity matrix
-  std::vector<std::vector<bool>> inv(cols);
-  for (i64 i = 0; i < cols; i++) {
-    inv[i].resize(cols);
-    inv[i][i] = 1;
+  // Each iteration computes x = (x * x^-1) mod poly.
+  for (i64 i = 0; i < 32; i++) {
+    x = std::rotl(x, 1);
+    x ^= (x & 1) * (poly << 1);
   }
 
-  for (i64 j = 0; j < rows; j++) {
-    u32 pos = 1 << j;
+  x ^= ~current;
 
-    if ((M[j] & pos) == 0) {
-      i64 k;
-      for (k = j + 1; k < cols; k++)
-        if (M[k] & pos)
-          break;
-
-      if (k == cols) {
-        std::cerr << "mold: internal error: crc32_solve: no solution\n";
-        exit(1);
-      }
-
-      std::swap(M[j], M[k]);
-      std::swap(inv[j], inv[k]);
-    }
-
-    for (i64 k = 0; k < cols; k++) {
-      if (k != j && (M[k] & pos)) {
-        M[k] ^= M[j];
-        for (i64 i = 0; i < cols; i++)
-          inv[k][i] = inv[k][i] ^ inv[j][i];
-      }
-    }
-  }
-
-  // multiply inverse by c to get result x
-  std::vector<bool> x(cols);
-  for (i64 j = 0; c; c >>= 1, j++)
-    if (c & 1)
-      for (i64 i = 0; i < cols; i++)
-        x[i] = x[i] ^ inv[j][i];
-  return x;
+  std::vector<u8> out(4);
+  out[0] = x;
+  out[1] = x >> 8;
+  out[2] = x >> 16;
+  out[3] = x >> 24;
+  return out;
 }
 
 // Compute a CRC for given data in parallel
@@ -168,30 +57,4 @@ u32 compute_crc32(u32 crc, u8 *buf, i64 len) {
   return crc;
 }
 
-// Given input data and a desired CRC value, this function returns
-// a binary blob such that if the blob is appended to the end of the
-// input data, the entire data's CRC value becomes the desired CRC.
-std::vector<u8> crc32_solve(i64 datalen, u32 current, u32 desired) {
-  // Compute the CRC for the given data and the all-zero trailer
-  constexpr i64 trailer_len = 16;
-  current = ~crc_zeros(~current, trailer_len);
-
-  // Compute CRCs for all bits in the trailer
-  std::vector<u32> mat;
-  for (i64 i = 0; i < trailer_len * 8; i++) {
-    u8 buf[trailer_len] = {};
-    buf[i / 8] = 1 << (i % 8);
-    mat.push_back(~crc32_z(~crc_zeros(0, datalen), buf, sizeof(buf)));
-  }
-
-  // Find desired trailer data
-  std::vector<bool> sol = gf2_matrix_solve(mat, desired ^ current);
-
-  std::vector<u8> out(trailer_len);
-  for (i64 i = 0; i < trailer_len * 8; i++)
-    if (sol[i])
-      out[i / 8] |= 1 << (i % 8);
-  return out;
-}
-
 } // namespace mold

elf/cmdline.cc

@@ -85,6 +85,8 @@ Options:
   --defsym=SYMBOL=VALUE       Define a symbol alias
   --demangle                  Demangle C++ symbols in log messages (default)
     --no-demangle
+  --detach                    Create separate debug info file in the background (default)
+    --no-detach
   --enable-new-dtags          Emit DT_RUNPATH for --rpath (default)
     --disable-new-dtags       Emit DT_RPATH for --rpath
   --execute-only              Make executable segments unreadable
@@ -759,6 +761,10 @@ std::vector<std::string> parse_nonpositional_args(Context<E> &ctx) {
       ctx.arg.demangle = true;
     } else if (read_flag("no-demangle")) {
       ctx.arg.demangle = false;
+    } else if (read_flag("detach")) {
+      ctx.arg.detach = true;
+    } else if (read_flag("no-detach")) {
+      ctx.arg.detach = false;
     } else if (read_flag("default-symver")) {
       ctx.arg.default_symver = true;
     } else if (read_flag("noinhibit-exec")) {
@@ -1413,6 +1419,10 @@ std::vector<std::string> parse_nonpositional_args(Context<E> &ctx) {
   if (ctx.arg.shared && warn_shared_textrel)
     ctx.arg.warn_textrel = true;
 
+  // We don't want the background process to write to stdout
+  if (ctx.arg.stats || ctx.arg.perf)
+    ctx.arg.detach = false;
+
   ctx.arg.undefined.push_back(ctx.arg.entry);
 
   for (i64 i = 0; i < ctx.arg.defsyms.size(); i++) {

elf/mold.h

@@ -1740,6 +1740,7 @@ struct Context {
     bool color_diagnostics = false;
     bool default_symver = false;
     bool demangle = true;
+    bool detach = true;
     bool discard_all = false;
     bool discard_locals = false;
     bool eh_frame_hdr = true;

elf/passes.cc

@@ -3058,7 +3058,7 @@ void write_separate_debug_file(Context<E> &ctx) {
 
   // We want to write to the debug info file in background so that the
   // user doesn't have to wait for it to complete.
-  if (!ctx.arg.stats && !ctx.arg.perf)
+  if (ctx.arg.detach)
     notify_parent();
 
   // A debug info file contains all sections as the original file, though
@@ -3102,13 +3102,13 @@ void write_separate_debug_file(Context<E> &ctx) {
   // Reverse-compute a CRC32 value so that the CRC32 checksum embedded to
   // the .gnu_debuglink section in the main executable matches with the
   // debug info file's CRC32 checksum.
-  std::vector<u8> &buf2 = ctx.output_file->buf2;
-  i64 datalen = filesize + buf2.size();
-
   u32 crc = compute_crc32(0, ctx.buf, filesize);
-  crc = compute_crc32(crc, buf2.data(), buf2.size());
 
-  std::vector<u8> trailer = crc32_solve(datalen, crc, ctx.gnu_debuglink->crc32);
+  std::vector<u8> &buf2 = ctx.output_file->buf2;
+  if (!buf2.empty())
+    crc = compute_crc32(crc, buf2.data(), buf2.size());
+
+  std::vector<u8> trailer = crc32_solve(crc, ctx.gnu_debuglink->crc32);
   append(ctx.output_file->buf2, trailer);
   ctx.output_file->close(ctx);
 }