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.
############### Attachment also inlined for ease of reply ###############
diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c index 76ab691b33e459a4ca80d337bdc70a1c53d6c1e0..c44e7aa458e2d28f2fefe1ec754482923c448d69 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;
@@ -6533,8 +6532,9 @@ 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