[xen staging] x86/EFI: keep debug info in xen.efi

[patchbot@xxxxxxx]

commit 1df03bc5958e3d8d1f2669426cd5b1353690505b
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Apr 26 10:25:10 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Apr 26 10:25:10 2021 +0200

    x86/EFI: keep debug info in xen.efi
    
    ... provided the linker supports it (which it does as of commit
    2dfa8341e079 ["ELF DWARF in PE output"]).
    
    Without mentioning debugging sections, the linker would put them at
    VA 0, thus making them unreachable by 32-bit (relative or absolute)
    relocations. If relocations were resolvable (or absent) the resulting
    binary would have invalid section RVAs (0 - __image_base__, truncated to
    32 bits). Mentioning debugging sections without specifying an address
    will result in the linker putting them all on the same RVA. A loader is,
    afaict, free to reject loading such an image, as sections shouldn't
    overlap. (The above describes GNU ld 2.36 behavior, which - if deemed
    buggy - could change.)
    
    Make sure our up-to-16Mb padding doesn't unnecessarily further extend
    the image.
    
    Take the opportunity and also switch to using $(call ld-option,...).
    
    Requested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/Makefile  | 13 ++++++++--
 xen/arch/x86/xen.lds.S | 68 +++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 75 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 5b47206ad1..ada085d17a 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -129,8 +129,14 @@ export XEN_BUILD_EFI := $(shell $(CC) $(XEN_CFLAGS) -c 
efi/check.c -o efi/check.
 CFLAGS-$(XEN_BUILD_EFI) += -DXEN_BUILD_EFI
 
 # Check if the linker supports PE.
-EFI_LDFLAGS = $(patsubst -m%,-mi386pep,$(XEN_LDFLAGS)) --subsystem=10 
--strip-debug
-XEN_BUILD_PE := $(if $(XEN_BUILD_EFI),$(shell $(LD) $(EFI_LDFLAGS) -o 
efi/check.efi efi/check.o 2>/dev/null && echo y))
+EFI_LDFLAGS = $(patsubst -m%,-mi386pep,$(XEN_LDFLAGS)) --subsystem=10
+XEN_BUILD_PE := $(if $(XEN_BUILD_EFI),$(call ld-option,$(EFI_LDFLAGS) 
--image-base=0x100000000 -o efi/check.efi efi/check.o))
+# If the above failed, it may be merely because of the linker not dealing well
+# with debug info. Try again with stripping it.
+ifeq ($(CONFIG_DEBUG_INFO)-$(XEN_BUILD_PE),y-n)
+EFI_LDFLAGS += --strip-debug
+XEN_BUILD_PE := $(call ld-option,$(EFI_LDFLAGS) --image-base=0x100000000 -o 
efi/check.efi efi/check.o)
+endif
 
 ifeq ($(XEN_BUILD_PE),y)
 
@@ -235,6 +241,9 @@ note_file_option ?= $(note_file)
 
 ifeq ($(XEN_BUILD_PE),y)
 $(TARGET).efi: prelink.o $(note_file) efi.lds efi/relocs-dummy.o efi/mkreloc
+ifeq ($(CONFIG_DEBUG_INFO),y)
+       $(if $(filter --strip-debug,$(EFI_LDFLAGS)),echo,:) "Will strip debug 
info from $(@F)"
+endif
        $(foreach base, $(VIRT_BASE) $(ALT_BASE), \
                  $(LD) $(call EFI_LDFLAGS,$(base)) -T efi.lds -N $< 
$(relocs-dummy) \
                        $(BASEDIR)/common/symbols-dummy.o $(note_file_option) 
-o $(@D)/.$(@F).$(base).0 &&) :
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 6346862250..bc53ee4597 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -312,10 +312,70 @@ SECTIONS
     *(.reloc)
     __base_relocs_end = .;
   }
-  /* Trick the linker into setting the image size to exactly 16Mb. */
-  . = ALIGN(__section_alignment__);
-  DECL_SECTION(.pad) {
-    . = ALIGN(MB(16));
+  /*
+   * Explicitly list debug section for the PE output so that they don't end
+   * up at VA 0 which is below image base and thus invalid. Also use the
+   * NOLOAD directive, despite currently ignored by ld for PE output, in
+   * order to record that we'd prefer these sections to not be loaded into
+   * memory.
+   *
+   * Note that we're past _end here, so if these sections get loaded they'll
+   * be discarded at runtime anyway.
+   */
+  .debug_abbrev ALIGN(1) (NOLOAD) : {
+     *(.debug_abbrev)
+  }
+  .debug_info ALIGN(1) (NOLOAD) : {
+    *(.debug_info)
+    *(.gnu.linkonce.wi.*)
+  }
+  .debug_types ALIGN(1) (NOLOAD) : {
+    *(.debug_types)
+  }
+  .debug_str ALIGN(1) (NOLOAD) : {
+    *(.debug_str)
+  }
+  .debug_line ALIGN(1) (NOLOAD) : {
+    *(.debug_line)
+    *(.debug_line.*)
+  }
+  .debug_line_str ALIGN(1) (NOLOAD) : {
+    *(.debug_line_str)
+  }
+  .debug_names ALIGN(4) (NOLOAD) : {
+    *(.debug_names)
+  }
+  .debug_frame ALIGN(4) (NOLOAD) : {
+    *(.debug_frame)
+  }
+  .debug_loc ALIGN(1) (NOLOAD) : {
+    *(.debug_loc)
+  }
+  .debug_loclists ALIGN(4) (NOLOAD) : {
+    *(.debug_loclists)
+  }
+  .debug_ranges ALIGN(8) (NOLOAD) : {
+    *(.debug_ranges)
+  }
+  .debug_rnglists ALIGN(4) (NOLOAD) : {
+    *(.debug_rnglists)
+  }
+  .debug_addr ALIGN(8) (NOLOAD) : {
+    *(.debug_addr)
+  }
+  .debug_aranges ALIGN(1) (NOLOAD) : {
+    *(.debug_aranges)
+  }
+  .debug_pubnames ALIGN(1) (NOLOAD) : {
+    *(.debug_pubnames)
+  }
+  .debug_pubtypes ALIGN(1) (NOLOAD) : {
+    *(.debug_pubtypes)
+  }
+  /* Trick the linker into setting the image size to no less than 16Mb. */
+  __image_end__ = .;
+  .pad ALIGN(__section_alignment__) : {
+    . = __image_end__ < __image_base__ + MB(16) ? ALIGN(MB(16)) : .;
   }
 #elif defined(XEN_BUILD_EFI)
   /*
--
generated by git-patchbot for /home/xen/git/xen.git#staging