scripts/specialize-patch: Rebuild filtered hunks

The regression became visible after commit 91517609cd
("scripts/generate-kernel-patch: Preserve split patches") preserved split
output that had previously been empty without diffstat.
specialize-patch kept the original hunk coordinates after dropping
version-dependent lines, so GNU patch rejected the generated qla.h patch.

Recalculate hunk coordinates and context after specialization removes added
lines. This prevents GNU patch from rejecting QLogic qla.h hunks for Linux
7.1 and 7.2.

Add a focused regression test for the normal and matching-line-number
specialization modes.

scripts/specialize-patch

@@ -613,21 +613,48 @@ function reset_hunk_state_variables() {
 function dump_lines() {
   # Detect empty hunks
   first_modif = -1
+  last_modif = -1
   for (i = 0; i < lines; i++)
   {
     if (line[i] ~ "^[+-]")
     {
-      first_modif = i
-      break
+      if (first_modif < 0)
+        first_modif = i
+      last_modif = i
     }
   }
 
   # Dump line[] as a hunk, but only if the hunk is not empty.
   if (first_modif >= 0)
   {
-    if (h[0] != "")
-      printf "@@ -%d,%d +%d,%d @@%s\n",h[1],h[2]-lines_less_deleted,h[3],h[4]-lines_less_added,h[5]
-    for (i = 0; i < lines; i++) {
+    # Restore standard unified diff context after discarding added lines.
+    first_line = first_modif > context_lines ? first_modif - context_lines : 0
+    last_line = last_modif + context_lines < lines ? \
+      last_modif + context_lines : lines - 1
+
+    if (h[0] != "") {
+      old_start = h[1]
+      new_start = h[3] + new_line_adjustment
+      for (i = 0; i < first_line; i++) {
+        if (line[i] !~ "^\\+" && line[i] !~ "^\\\\")
+          old_start++
+        if (line[i] !~ "^-" && line[i] !~ "^\\\\")
+          new_start++
+      }
+
+      old_count = 0
+      new_count = 0
+      for (i = first_line; i <= last_line; i++) {
+        if (line[i] !~ "^\\+" && line[i] !~ "^\\\\")
+          old_count++
+        if (line[i] !~ "^-" && line[i] !~ "^\\\\")
+          new_count++
+      }
+
+      printf "@@ -%d,%d +%d,%d @@%s\n", old_start, old_count, \
+        new_start, new_count, h[5]
+    }
+    for (i = first_line; i <= last_line; i++) {
       modifier = (LINUX_VERSION_CODE < version_code("4.19.0") &&
                   (RHEL_MAJOR == "" ||
                    RHEL_MAJOR * 256 + RHEL_MINOR < 7 * 256 + 7 ||
@@ -638,6 +665,9 @@ function dump_lines() {
       print line[i]
     }
   }
+
+  if (h[0] != "")
+    new_line_adjustment += lines_less_deleted - lines_less_added
 }
 
 BEGIN {
@@ -660,6 +690,7 @@ BEGIN {
   if (config_tcp_zero_copy_transfer_completion_notification_undefined != 0 && config_tcp_zero_copy_transfer_completion_notification_undefined != 1)
     config_tcp_zero_copy_transfer_completion_notification_undefined = 0
   # Variable initialization.
+  context_lines = 3
   process_file = 0
   reset_hunk_state_variables()
 }
@@ -667,11 +698,13 @@ BEGIN {
 
 {
   if (match($0, "^diff[ \t]+[^ \t]+[ \t]+[^ \t]+[ \t]+([^ \t]+)$", filename) \
+      || match($0, "^---[ \t]+([^ \t]+)[ \t]+", filename) \
       || match($0, "^\\+\\+\\+[ \t]+([^ \t]+)[ \t]+", filename))
   {
     # Start of new file.
     dump_lines()
     reset_hunk_state_variables()
+    new_line_adjustment = 0
     process_file = match(filename[1], "\\.[ch]$") != 0 &&
       match(filename[1], "drivers/scsi/qla2xxx/") == 0
   }

scripts/test-specialize-patch

@@ -0,0 +1,116 @@
+#!/bin/bash
+
+set -euo pipefail
+
+script_dir="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
+scst_dir="$(dirname -- "$script_dir")"
+test_dir="$(mktemp -d)"
+
+trap 'rm -rf -- "$test_dir"' EXIT
+
+mkdir -p "$test_dir/orig"
+
+cat > "$test_dir/orig/qla.h" <<'EOF'
+/* SPDX-License-Identifier: GPL-2.0 */
+#if !defined(_TRACE_QLA_H_) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_QLA_H_
+
+#include <linux/tracepoint.h>
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM qla
+
+#define QLA_MSG_MAX 256
+
+#pragma GCC diagnostic push
+#ifndef __clang__
+#pragma GCC diagnostic ignored "-Wsuggest-attribute=format"
+#endif
+
+DECLARE_EVENT_CLASS(qla_log_event,
+	TP_PROTO(const char *buf,
+		struct va_format *vaf),
+
+	TP_ARGS(buf, vaf),
+
+	TP_STRUCT__entry(
+		__string(buf, buf)
+		__vstring(msg, vaf->fmt, vaf->va)
+	),
+	TP_fast_assign(
+		__assign_str(buf);
+		__assign_vstr(msg, vaf->fmt, vaf->va);
+	),
+
+	TP_printk("%s %s", __get_str(buf), __get_str(msg))
+);
+
+#pragma GCC diagnostic pop
+
+DEFINE_EVENT(qla_log_event, ql_dbg_log,
+	TP_PROTO(const char *buf, struct va_format *vaf),
+	TP_ARGS(buf, vaf)
+);
+
+#endif /* _TRACE_QLA_H */
+
+#define TRACE_INCLUDE_FILE qla
+
+#include <trace/define_trace.h>
+EOF
+
+if diff -up "$test_dir/orig/qla.h" \
+  "$scst_dir/qla2x00t-32gbit/include/trace/events/qla.h" \
+  > "$test_dir/qla.raw.patch"; then
+  echo "Error: qla.h test inputs do not differ." >&2
+  exit 1
+else
+  diff_status=$?
+  if [ "$diff_status" -gt 1 ]; then
+    exit "$diff_status"
+  fi
+fi
+
+for kernel_version in 7.1 7.2; do
+  mkdir -p "$test_dir/linux-$kernel_version/include/trace/events"
+  cp "$test_dir/orig/qla.h" \
+    "$test_dir/linux-$kernel_version/include/trace/events/qla.h"
+
+  sed -e "s:^--- [^ ]*:--- linux-$kernel_version/include/trace/events/qla.h:" \
+    -e "s:^+++ [^ ]*:+++ linux-$kernel_version/include/trace/events/qla.h:" \
+    < "$test_dir/qla.raw.patch" > "$test_dir/qla-$kernel_version.patch"
+
+  cat >> "$test_dir/qla-$kernel_version.patch" <<EOF
+--- linux-$kernel_version/drivers/scst/next.c 2026-08-26 00:00:00.000000000 +0300
++++ linux-$kernel_version/drivers/scst/next.c 2026-08-26 00:00:00.000000000 +0300
+@@ -1,1 +1,1 @@
+-old
++new
+EOF
+
+  mkdir -p "$test_dir/linux-$kernel_version/drivers/scst"
+  echo old > "$test_dir/linux-$kernel_version/drivers/scst/next.c"
+
+  "$script_dir/specialize-patch" -v delete_disabled_code=1 \
+    -v kernel_version="$kernel_version" -v SCST_IO_CONTEXT=0 \
+    < "$test_dir/qla-$kernel_version.patch" \
+    > "$test_dir/qla-$kernel_version.specialized.patch"
+
+  grep -qF '@@ -9,8 +9,8 @@' \
+    "$test_dir/qla-$kernel_version.specialized.patch"
+  grep -qF '@@ -32,13 +32,15 @@' \
+    "$test_dir/qla-$kernel_version.specialized.patch"
+
+  patch --dry-run -f -s -p0 -d "$test_dir" \
+    < "$test_dir/qla-$kernel_version.specialized.patch"
+
+  "$script_dir/specialize-patch" -v blank_deleted_code=1 \
+    -v kernel_version="$kernel_version" -v SCST_IO_CONTEXT=0 \
+    < "$test_dir/qla-$kernel_version.patch" \
+    > "$test_dir/qla-$kernel_version.specialized-n.patch"
+
+  patch --dry-run -f -s -p0 -d "$test_dir" \
+    < "$test_dir/qla-$kernel_version.specialized-n.patch"
+done
+
+echo "specialize-patch qla.h regression: PASS"