[PATCH v4 06/15] gdb: Add functions to make loading from dynamically positioned targets easier

[Glenn Washburn]

Many targets, such as EFI, load GRUB at addresses that are determined at
runtime. So the load addresses in kernel.exec will almost certainly be
wrong. Given the address of the start of the text segment, these
functions will tell GDB to load the symbols at the proper locations. It
is left up to the user to determine how to get the text address.

Signed-off-by: Glenn Washburn <development@efficientek.com>
---
 grub-core/Makefile.core.def |  6 ++++
 grub-core/gdb_grub.in       | 27 ++++++++++++++++
 grub-core/gdb_helper.sh.in  | 62 +++++++++++++++++++++++++++++++++++++
 3 files changed, 95 insertions(+)
 create mode 100644 grub-core/gdb_helper.sh.in

diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index 95942fc8c9..253b9b1e47 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -24,6 +24,12 @@ transform_data = {
   common = gmodule.pl.in;
 };
 
+transform_data = {
+  installdir = platform;
+  name = gdb_helper.sh;
+  common = gdb_helper.sh.in;
+};
+
 transform_data = {
   installdir = platform;
   name = gdb_grub;
diff --git a/grub-core/gdb_grub.in b/grub-core/gdb_grub.in
index 1fb9603ff8..d97dbfdc0d 100644
--- a/grub-core/gdb_grub.in
+++ b/grub-core/gdb_grub.in
@@ -9,6 +9,33 @@
 ### Lubomir Kundrak <lkudrak@skosi.org>
 ###
 
+define dynamic_load_kernel_exec_symbols
+       shell rm -f .remove-kernel.exec.symfile.gdb
+       shell sh gdb_helper.sh gen_kernel_exec_loadsym $arg0 
>.kernel.exec.loadsym.gdb
+       source .kernel.exec.loadsym.gdb
+end
+document dynamic_load_kernel_exec_symbols
+       Load debugging symbols from kernel.exec given the address of the
+       .text segment of the UEFI binary in memory.
+end
+
+define dynamic_load_symbols
+       dynamic_load_kernel_exec_symbols $arg0
+
+       # We may have been very late to loading the kernel.exec symbols and
+       # and modules may already be loaded. So load symbols for any already
+       # loaded.
+       load_all_modules
+
+       runtime_load_module
+end
+document dynamic_load_symbols
+       Load debugging symbols from kernel.exec and any loaded modules given
+       the address of the .text segment of the UEFI binary in memory. Also
+       setup session to automatically load module symbols for modules loaded
+       in the future.
+end
+
 # Add section numbers and addresses to .segments.tmp
 define dump_module_sections_helper
        set $mod = $arg0
diff --git a/grub-core/gdb_helper.sh.in b/grub-core/gdb_helper.sh.in
new file mode 100644
index 0000000000..b37d5adfc2
--- /dev/null
+++ b/grub-core/gdb_helper.sh.in
@@ -0,0 +1,62 @@
+###
+### Helper functions for GRUB's GDB script.
+###
+
+alignup() {
+  PAD=1
+  if [ "$(($1%$2))" -eq 0 ]; then
+    PAD=0
+  fi
+  printf "0x%x\n" "$(((($1/$2)+$PAD)*$2))"
+}
+
+exp() {
+  BASE=${1%%\*\**}
+  EXP=${1##*\*\*}
+  RES=1
+  while [ "$EXP" -gt 0 ]; do
+    RES=$(($RES*$BASE))
+    EXP=$(($EXP - 1))
+  done
+  echo $RES
+}
+
+# Loading symbols is complicated by the fact that kernel.exec is an ELF
+# ELF binary, but the UEFI runtime is PE32+. All the data sections of
+# the ELF binary are concatenated (accounting for ELF section alignment)
+# and put into one .data section in the PE32+ runtime image. So given
+# the load address of the .data PE32+ section we can determine the
+# addresses each ELF data section maps to. The UEFI application is
+# loaded into memory just as it is laid out in the file. It is not
+# assumed that the binary is available, but it is known that the .text
+# section directly precedes the .data section and that .data is EFI
+# page aligned. Using this, the .data offset from .text can be found.
+gen_kernel_exec_loadsym() {
+  PE_SECTION_ALIGN=$((1<<12))
+  PE_TEXT=$1
+  TSIZE=$((0x$(objdump -h kernel.exec | grep -E " \.text\b" | \
+                  (read _ _ SIZE _; echo $SIZE))))
+  PE_DATA_OFF=$(printf "0x%x" $(($(alignup ${TSIZE} ${PE_SECTION_ALIGN}))))
+
+  printf "add-symbol-file kernel.exec ${PE_TEXT}"
+  objdump -h kernel.exec | tail -n +6 | \
+    while read IDX NAME SIZE _ _ OFFSET ALIGN; do
+      read FLAGS
+      if [ -n "$FLAGS" ] && [ -z "${FLAGS%%*DATA*}" -o "$NAME" = .bss ]; then
+        OFF=$(alignup ${OFF:-0} $(exp $ALIGN))
+       printf " -s $NAME (${PE_TEXT}+${PE_DATA_OFF}+0x%x)" "$OFF"
+        OFF=$((${OFF} + 0x${SIZE}))
+      fi
+    done
+}
+
+if type "$1" 2>/dev/null | grep -q 'is a shell function'; then
+  if [ "x${GRUB_GDB_TRACE}" = "xy" ]; then
+    exec 2>>gdb_helper.trace
+    set -x
+  fi
+
+  "$@"
+else
+  exit 1
+fi
-- 
2.34.1