From: Matthew Malcomson <matthew.malcomson@arm.com>
Date: Thu, 10 Feb 2022 18:15:47 +0000 (+0000)
Subject: Return the alignment required from c64_valid_cap_range
X-Git-Url: http://git.ipfire.org/?p=thirdparty%2Fbinutils-gdb.git;a=commitdiff_plain;h=5a9e7a184dd05b707113ed5a2890241c8fa2be36

Return the alignment required from c64_valid_cap_range

We were specifying section alignment requirements based on the alignment
that the section base happened to have.  This sometimes resulted in very
strange alignment requests that were much greater than actually
required.
That is not usually a problem, but it does give unnecessary padding upon
re-adjustments due to changing the PCC bounds after individual sections
have been padded.

This patch adds an interface such that we return the alignment actually
required for exact capability bounds from c64_valid_cap_range.  We then
use that alignment as our alignment requirement on the sections which
have a section-sized symbol associated with them.
---

diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
index 0a455763fae..12aaa5bf764 100644
--- a/bfd/elfnn-aarch64.c
+++ b/bfd/elfnn-aarch64.c
@@ -4801,11 +4801,12 @@ exponent (uint64_t len)
 #define ALIGN_UP(x, a)  (((x) + ONES (a)) & (~ONES (a)))
 
 static bfd_boolean
-c64_valid_cap_range (bfd_vma *basep, bfd_vma *limitp)
+c64_valid_cap_range (bfd_vma *basep, bfd_vma *limitp, unsigned *alignmentp)
 {
   bfd_vma base = *basep, size = *limitp - *basep;
 
   unsigned e, old_e;
+  *alignmentp = 1;
 
   if ((e = exponent (size)) == (unsigned) -1)
     return TRUE;
@@ -4818,6 +4819,7 @@ c64_valid_cap_range (bfd_vma *basep, bfd_vma *limitp)
 
   base = ALIGN_UP (base, e + 3);
 
+  *alignmentp = e+3;
   if (base == *basep && *limitp == base + size)
     return TRUE;
 
@@ -4868,17 +4870,18 @@ record_section_change (asection *sec, struct sec_change_queue **queue)
 {
   bfd_vma low = sec->vma;
   bfd_vma high = sec->vma + sec->size;
+  unsigned alignment;
 
-  if (!c64_valid_cap_range (&low, &high))
+  if (!c64_valid_cap_range (&low, &high, &alignment))
     queue_section_padding (queue, sec);
 }
 
 /* Make sure that all capabilities that refer to sections have bounds that
    won't overlap with neighbouring sections.  This is needed in two specific
    cases.  The first case is that of PCC, which needs to span across all
-   executable sections as well as the GOT and PLT sections in the output
-   binary.  The second case is that of linker and ldscript defined symbols that
-   indicate start and/or end of sections.
+   readonly sections as well as the GOT and PLT sections in the output binary.
+   The second case is that of linker and ldscript defined symbols that indicate
+   start and/or end of sections and/or zero-sized symbols.
 
    In both cases, overlap of capability bounds are avoided by aligning the base
    of the section and if necessary, adding a pad at the end of the section so
@@ -4963,7 +4966,6 @@ elfNN_c64_resize_sections (bfd *output_bfd, struct bfd_link_info *info,
 		  if (len > 8 && name[0] == '_' && name[1] == '_'
 		      && (!strncmp (name + 2, "start_", 6)
 			  || !strcmp (name + len - 6, "_start")))
-
 		    {
 		      bfd_vma value = os->vma + os->size;
 
@@ -5029,10 +5031,8 @@ elfNN_c64_resize_sections (bfd *output_bfd, struct bfd_link_info *info,
       low = queue->sec->vma;
       high = queue->sec->vma + queue->sec->size;
 
-      if (!c64_valid_cap_range (&low, &high))
+      if (!c64_valid_cap_range (&low, &high, &align))
 	{
-	  align = __builtin_ctzl (low);
-
 	  if (queue->sec->alignment_power < align)
 	    queue->sec->alignment_power = align;
 
@@ -5057,9 +5057,8 @@ elfNN_c64_resize_sections (bfd *output_bfd, struct bfd_link_info *info,
 	  pcc_low = pcc_low_sec->vma;
 	  pcc_high = pcc_high_sec->vma + pcc_high_sec->size + padding;
 
-	  if (!c64_valid_cap_range (&pcc_low, &pcc_high))
+	  if (!c64_valid_cap_range (&pcc_low, &pcc_high, &align))
 	    {
-	      align = __builtin_ctzl (pcc_low);
 	      if (pcc_low_sec->alignment_power < align)
 		pcc_low_sec->alignment_power = align;
 
@@ -6514,8 +6513,9 @@ c64_fixup_frag (bfd *input_bfd, struct bfd_link_info *info,
     return bfd_reloc_outofrange;
 
   bfd_vma base = value, limit = value + size;
+  unsigned align = 0;
 
-  if (!bounds_ok && !c64_valid_cap_range (&base, &limit))
+  if (!bounds_ok && !c64_valid_cap_range (&base, &limit, &align))
     {
       /* Just warn about this.  It's not a requirement that bounds on
 	 objects should be precise, so there's no reason to error out on