Simplify updating libbacktrace

Previously our `regenerate_libbacktrace.sh` script could only clone the
repo and re-apply our existing patches. Give it the ability to also
update to a different commit and rebase our patches.

If the rebasing fails, have it leave the `.git` directory around so that
a developer can manually rebase and finish the job.

Signed-off-by: Matt Wozniski <[email protected]>

src/vendor/libbacktrace_7e2b7da3d6568d2e4e78658f22e701746a48d7e1_patch.diff → src/vendor/libbacktrace-patches/0001-Expose-some-internal-functions-of-libbacktrace.patch

@@ -1,3 +1,17 @@
+From d99c0a30bacfe6cae604a85250f12587d0fee932 Mon Sep 17 00:00:00 2001
+From: Matt Wozniski <[email protected]>
+Date: Thu, 25 Jul 2024 18:59:09 -0400
+Subject: [PATCH] Expose some internal functions of libbacktrace
+
+Memray uses these for more control than the public entry points give.
+---
+ Makefile.am |  2 +-
+ Makefile.in |  2 +-
+ elf.c       | 10 +++++-----
+ internal.h  | 39 +++++++++++++++++++++++++++++++++++++++
+ macho.c     | 31 +++++++++++++++++++------------
+ 5 files changed, 65 insertions(+), 19 deletions(-)
+
 diff --git a/Makefile.am b/Makefile.am
 index 4d509a2..f80a9e6 100644
 --- a/Makefile.am
@@ -224,3 +238,6 @@ index fc4c959..527c5ac 100644
        break;
      default:
        error_callback (data, "executable file is not an executable", 0);
+-- 
+2.42.3
+

src/vendor/libbacktrace_7e2b7da3d6568d2e4e78658f22e701746a48d7e1_debuginfod_patch.diff → src/vendor/libbacktrace-patches/0002-Add-debuginfod-support-to-libbacktrace.patch

@@ -1,3 +1,17 @@
+From b052eda140ac673de19a3060523fb250d898ffb6 Mon Sep 17 00:00:00 2001
+From: Matt Wozniski <[email protected]>
+Date: Thu, 25 Jul 2024 18:59:10 -0400
+Subject: [PATCH] Add debuginfod support to libbacktrace
+
+Allow fetching debug info from a debuginfod server when unwinding.
+---
+ Makefile.am          |   5 +-
+ Makefile.in          |   5 +-
+ debuginfod_support.h | 115 +++++++++++++++++++++++++++++++++++++++++++
+ elf.c                |  64 ++++++++++++++++++++++++
+ 4 files changed, 185 insertions(+), 4 deletions(-)
+ create mode 100644 debuginfod_support.h
+
 diff --git a/Makefile.am b/Makefile.am
 index f80a9e6..15e87c7 100644
 --- a/Makefile.am
@@ -283,3 +297,6 @@ index 80482a4..61f08af 100644
 
    if (!state->threaded)
      {
+-- 
+2.42.3
+

src/vendor/regenerate_libbacktrace.sh

@@ -1,23 +1,39 @@
 #!/usr/bin/env bash
 set -Eeuo pipefail
 
-SNAPSHOT_COMMIT=7e2b7da3d6568d2e4e78658f22e701746a48d7e1
-LIBBACKTRACE_DIR="libbacktrace"
+if [[ $# -ne 0 ]] && [[ $# -ne 1 ]]; then
+    echo "Usage: $0 [new-commit]"
+    exit 1
+fi
 
-echo "checking" $(ls)
+old_snapshot=7e2b7da3d6568d2e4e78658f22e701746a48d7e1
+new_snapshot=${1:-}
 
 echo ">>> Cloning libbacktrace"
-rm -rf "$LIBBACKTRACE_DIR"
-git clone https://github.com/ianlancetaylor/libbacktrace.git "$LIBBACKTRACE_DIR"
+rm -rf libbacktrace
+git clone https://github.com/ianlancetaylor/libbacktrace.git libbacktrace
 
-echo ">>> Checking out commit ${SNAPSHOT_COMMIT}"
-cd "$LIBBACKTRACE_DIR"
-git checkout $SNAPSHOT_COMMIT 1>/dev/null
+echo "Applying patches"
+cd libbacktrace
+git checkout "$old_snapshot"
+git am ../libbacktrace-patches/*
+
+if [[ -n "$new_snapshot" ]]; then
+    echo "Rebasing on $new_snapshot"
+    if git rebase "$new_snapshot"; then
+        echo "Rebased successfully. Updating patches."
+        (cd ../libbacktrace-patches && git rm -f 0*)
+        git format-patch "$new_snapshot" --no-numbered --output-directory=../libbacktrace-patches
+        (cd ../libbacktrace-patches && git add 0*)
+    else
+        echo "Failed to apply patches. You must finish rebasing manually."
+        echo "When you are satisfied, update the patches by running:"
+        echo "  git format-patch $new_snapshot --no-numbered --output-directory=../libbacktrace-patches"
+        echo "Be sure to remove the old patches first if the file names will change."
+        exit 1
+    fi
+fi
 
-echo ">>> Applying main patch for commit ${SNAPSHOT_COMMIT}"
-git apply ../libbacktrace_${SNAPSHOT_COMMIT}_patch.diff
-echo ">>> Applying debuginfod patch for commit ${SNAPSHOT_COMMIT}"
-git apply ../libbacktrace_${SNAPSHOT_COMMIT}_debuginfod_patch.diff
 rm -rf .git
 
 echo "Regenerated vendored libbacktrace"