+/*
+ * We're writing a section table for a few reasons:
+ *
+ * The Go runtime had a couple of bugs: it would read the section
+ * table to try to figure out how many dynamic symbols there were (it
+ * shouldn't have looked at the section table at all) and, if there
+ * were no SHT_SYNDYM section table entry, it would use an
+ * uninitialized value for the number of symbols. An empty DYNSYM
+ * table would work, but I see no reason not to write a valid one (and
+ * keep full performance for old Go programs). This hack is only
+ * needed on x86_64.
+ *
+ * The bug was introduced on 2012-08-31 by:
+ * https://code.google.com/p/go/source/detail?r=56ea40aac72b
+ * and was fixed on 2014-06-13 by:
+ * https://code.google.com/p/go/source/detail?r=fc1cd5e12595
+ *
+ * Binutils has issues debugging the vDSO: it reads the section table to
+ * find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which
+ * would break build-id if we removed the section table. Binutils
+ * also requires that shstrndx != 0. See:
+ * https://sourceware.org/bugzilla/show_bug.cgi?id=17064
+ *
+ * elfutils might not look for PT_NOTE if there is a section table at
+ * all. I don't know whether this matters for any practical purpose.
+ *
+ * For simplicity, rather than hacking up a partial section table, we
+ * just write a mostly complete one. We omit non-dynamic symbols,
+ * though, since they're rather large.
+ *
+ * Once binutils gets fixed, we might be able to drop this for all but
+ * the 64-bit vdso, since build-id only works in kernel RPMs, and
+ * systems that update to new enough kernel RPMs will likely update
+ * binutils in sync. build-id has never worked for home-built kernel
+ * RPMs without manual symlinking, and I suspect that no one ever does
+ * that.
+ */
+struct BITSFUNC(fake_sections)
+{
+ ELF(Shdr) *table;
+ unsigned long table_offset;
+ int count, max_count;
+
+ int in_shstrndx;
+ unsigned long shstr_offset;
+ const char *shstrtab;
+ size_t shstrtab_len;
+
+ int out_shstrndx;
+};
+
+static unsigned int BITSFUNC(find_shname)(struct BITSFUNC(fake_sections) *out,
+ const char *name)
+{
+ const char *outname = out->shstrtab;
+ while (outname - out->shstrtab < out->shstrtab_len) {
+ if (!strcmp(name, outname))
+ return (outname - out->shstrtab) + out->shstr_offset;
+ outname += strlen(outname) + 1;
+ }
+
+ if (*name)
+ printf("Warning: could not find output name \"%s\"\n", name);
+ return out->shstr_offset + out->shstrtab_len - 1; /* Use a null. */
+}
+
+static void BITSFUNC(init_sections)(struct BITSFUNC(fake_sections) *out)
+{
+ if (!out->in_shstrndx)
+ fail("didn't find the fake shstrndx\n");
+
+ memset(out->table, 0, out->max_count * sizeof(ELF(Shdr)));
+
+ if (out->max_count < 1)
+ fail("we need at least two fake output sections\n");
+
+ PUT_LE(&out->table[0].sh_type, SHT_NULL);
+ PUT_LE(&out->table[0].sh_name, BITSFUNC(find_shname)(out, ""));
+
+ out->count = 1;
+}
+
+static void BITSFUNC(copy_section)(struct BITSFUNC(fake_sections) *out,
+ int in_idx, const ELF(Shdr) *in,
+ const char *name)
+{
+ uint64_t flags = GET_LE(&in->sh_flags);
+
+ bool copy = flags & SHF_ALLOC &&
+ (GET_LE(&in->sh_size) ||
+ (GET_LE(&in->sh_type) != SHT_RELA &&
+ GET_LE(&in->sh_type) != SHT_REL)) &&
+ strcmp(name, ".altinstructions") &&
+ strcmp(name, ".altinstr_replacement");
+
+ if (!copy)
+ return;
+
+ if (out->count >= out->max_count)
+ fail("too many copied sections (max = %d)\n", out->max_count);
+
+ if (in_idx == out->in_shstrndx)
+ out->out_shstrndx = out->count;
+
+ out->table[out->count] = *in;
+ PUT_LE(&out->table[out->count].sh_name,
+ BITSFUNC(find_shname)(out, name));
+
+ /* elfutils requires that a strtab have the correct type. */
+ if (!strcmp(name, ".fake_shstrtab"))
+ PUT_LE(&out->table[out->count].sh_type, SHT_STRTAB);
+
+ out->count++;
+}
+
+static void BITSFUNC(go)(void *addr, size_t len,
+ FILE *outfile, const char *name)