NOBITS expansion, for .bss etc

GNU binutils' readelf gets confused with symbol versions. More analysis
needed on that.

1 files changed, 116 insertions, 0 deletions

diff --git a/src/model/expandNobits.c b/src/model/expandNobits.c
new file mode 100644
index 0000000..7c14668
--- /dev/null
+++ b/src/model/expandNobits.c
@@ -0,0 +1,116 @@
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <gelf.h>
+#include <libelfu/libelfu.h>
+
+
+void elfu_mExpandNobits(ElfuElf *me, GElf_Off off)
+{
+  ElfuScn *ms;
+  ElfuPhdr *mp;
+  GElf_Xword expansionSize;
+
+  assert(me);
+
+  expansionSize = 0;
+
+  /* Find the maximum amount we need to expand by. Check PHDRs first */
+  CIRCLEQ_FOREACH(mp, &me->phdrList, elem) {
+    GElf_Off off2 = mp->phdr.p_offset;
+    GElf_Off end2 = mp->phdr.p_offset + mp->phdr.p_filesz;
+    if (end2 == off) {
+      GElf_Xword size2 = mp->phdr.p_memsz - mp->phdr.p_filesz;
+      if (size2 > expansionSize) {
+        expansionSize = size2;
+      }
+    } else if (end2 > off) {
+      if (off2 < off) {
+        /*
+         * Found a PHDR whose file contents overlaps with the section
+         * to be filled. This means that it relies on the NOBITS area
+         * being actually 0 bytes, and the expansion would ruin it.
+         */
+        fprintf(stderr, "mExpandNobits: Found PHDR spanning expansion offset. Aborting.\n");
+        return;
+      }
+    } else {
+      // end2 < off, and the PHDR is unaffected.
+      continue;
+    }
+  }
+
+  /* Now check SHDRs */
+  CIRCLEQ_FOREACH(ms, &me->scnList, elem) {
+    if (ms->shdr.sh_offset == off) {
+      if (ms->shdr.sh_type == SHT_NOBITS) {
+        if (ms->shdr.sh_size > expansionSize) {
+          expansionSize = ms->shdr.sh_size;
+        }
+      }
+    }
+  }
+
+
+
+  /* Expand! */
+
+
+  /* Move all following PHDR offsets further down the file. */
+  CIRCLEQ_FOREACH(mp, &me->phdrList, elem) {
+    GElf_Off off2 = mp->phdr.p_offset;
+    GElf_Off end2 = mp->phdr.p_offset + mp->phdr.p_filesz;
+
+    if (off2 >= off) {
+      mp->phdr.p_offset += expansionSize;
+    } else {
+      if (end2 == off) {
+        /* This PHDR now has corresponding bytes in the file for every
+         * byte in memory. */
+        mp->phdr.p_filesz = mp->phdr.p_memsz;
+      }
+    }
+  }
+
+  /* Move the following sections */
+  CIRCLEQ_FOREACH(ms, &me->scnList, elem) {
+    if (ms->shdr.sh_offset >= off) {
+      if (ms->shdr.sh_offset > off
+          || ms->shdr.sh_type != SHT_NOBITS) {
+        ms->shdr.sh_offset += expansionSize;
+      }
+    }
+  }
+
+  /* Move SHDR/PHDR tables */
+  if (me->ehdr.e_shoff >= off) {
+    me->ehdr.e_shoff += expansionSize;
+  }
+
+  if (me->ehdr.e_phoff >= off) {
+    me->ehdr.e_phoff += expansionSize;
+  }
+
+
+  /* Convert any NOBITS at off to PROGBITS */
+  CIRCLEQ_FOREACH(ms, &me->scnList, elem) {
+    if (ms->shdr.sh_offset == off) {
+      if (ms->shdr.sh_type == SHT_NOBITS) {
+        ms->data.d_buf = malloc(ms->shdr.sh_size);
+        memset(ms->data.d_buf, '\0', ms->shdr.sh_size);
+        if (!ms->data.d_buf) {
+          fprintf(stderr, "mExpandNobits: Could not allocate %jd bytes for NOBITS expansion.\n", ms->shdr.sh_size);
+        }
+
+        ms->data.d_align = 1;
+        ms->data.d_off  = 0;
+        ms->data.d_type = ELF_T_BYTE;
+        ms->data.d_size = ms->shdr.sh_size;
+        ms->data.d_version = elf_version(EV_NONE);
+
+        ms->shdr.sh_type = SHT_PROGBITS;
+      }
+    }
+  }
+}