linker: add LD_SHOW_AUXV support.
Yes, `od -t d8 /proc/self/auxv` is clever:
```
$ adb shell od -t d8 /proc/self/auxv
0000000 33 488593047552
0000020 51 4720
0000040 16 1155071
0000060 6 4096
0000100 17 100
0000120 3 375971917888
0000140 4 56
0000160 5 12
0000200 7 488593051648
0000220 8 0
0000240 9 375972184064
0000260 11 0
0000300 12 0
0000320 13 0
0000340 14 0
0000360 23 0
0000400 25 549220780840
0000420 26 0
0000440 31 549220786153
0000460 15 549220780856
0000500 0 0
0000520
$
```
But this is a lot easier to read:
```
$ adb shell LD_SHOW_AUXV=1 date
AT_SYSINFO_EHDR 0x7065010000
AT_MINSIGSTKSZ 4720
AT_HWCAP 0b100011001111111111111
AT_PAGESZ 4096
AT_CLKTCK 100
AT_PHDR 0x5c79d60040
AT_PHENT 56
AT_PHNUM 12
AT_BASE 0x7065011000
AT_FLAGS 0
AT_ENTRY 0x5c79da1000
AT_UID 0
AT_EUID 0
AT_GID 0
AT_EGID 0
AT_SECURE 0
AT_RANDOM 0x7ff814eb98
AT_HWCAP2 0
AT_EXECFN "/system/bin/date"
AT_PLATFORM "aarch64"
Tue Aug 22 20:43:22 GMT 2023
```
Test: adb shell LD_SHOW_AUXV=1 date
Change-Id: I51c4e8cbb799eb1dc360c9417cc6f82bebdcda73
diff --git a/linker/linker_auxv.cpp b/linker/linker_auxv.cpp
new file mode 100644
index 0000000..d8e4a3e
--- /dev/null
+++ b/linker/linker_auxv.cpp
@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "linker_auxv.h"
+
+#include <elf.h>
+#include <stdio.h>
+#include <sys/auxv.h>
+#include <unistd.h>
+
+#include <async_safe/log.h>
+
+static const char* auxv_name(int at) {
+ switch (at) {
+ case AT_NULL: return "AT_NULL";
+ case AT_IGNORE: return "AT_IGNORE";
+ case AT_EXECFD: return "AT_EXECFD";
+ case AT_PHDR: return "AT_PHDR";
+ case AT_PHENT: return "AT_PHENT";
+ case AT_PHNUM: return "AT_PHNUM";
+ case AT_PAGESZ: return "AT_PAGESZ";
+ case AT_BASE: return "AT_BASE";
+ case AT_FLAGS: return "AT_FLAGS";
+ case AT_ENTRY: return "AT_ENTRY";
+ case AT_NOTELF: return "AT_NOTELF";
+ case AT_UID: return "AT_UID";
+ case AT_EUID: return "AT_EUID";
+ case AT_GID: return "AT_GID";
+ case AT_EGID: return "AT_EGID";
+ case AT_PLATFORM: return "AT_PLATFORM";
+ case AT_HWCAP: return "AT_HWCAP";
+ case AT_CLKTCK: return "AT_CLKTCK";
+ case AT_SECURE: return "AT_SECURE";
+ case AT_BASE_PLATFORM: return "AT_BASE_PLATFORM";
+ case AT_RANDOM: return "AT_RANDOM";
+ case AT_HWCAP2: return "AT_HWCAP2";
+ case AT_RSEQ_FEATURE_SIZE: return "AT_RSEQ_FEATURE_SIZE";
+ case AT_RSEQ_ALIGN: return "AT_RSEQ_ALIGN";
+ case AT_EXECFN: return "AT_EXECFN";
+ case AT_SYSINFO_EHDR: return "AT_SYSINFO_EHDR";
+#if defined(AT_MINSIGSTKSZ)
+ case AT_MINSIGSTKSZ: return "AT_MINSIGSTKSZ";
+#endif
+#if defined(AT_SYSINFO)
+ case AT_SYSINFO: return "AT_SYSINFO";
+#endif
+#if defined(AT_L1I_CACHESIZE)
+ case AT_L1I_CACHESIZE: return "AT_L1I_CACHESIZE";
+#endif
+#if defined(AT_L1I_CACHEGEOMETRY)
+ case AT_L1I_CACHEGEOMETRY: return "AT_L1I_CACHEGEOMETRY";
+#endif
+#if defined(AT_L1D_CACHESIZE)
+ case AT_L1D_CACHESIZE: return "AT_L1D_CACHESIZE";
+#endif
+#if defined(AT_L1D_CACHEGEOMETRY)
+ case AT_L1D_CACHEGEOMETRY: return "AT_L1D_CACHEGEOMETRY";
+#endif
+#if defined(AT_L2_CACHESIZE)
+ case AT_L2_CACHESIZE: return "AT_L2_CACHESIZE";
+#endif
+#if defined(AT_L2_CACHEGEOMETRY)
+ case AT_L2_CACHEGEOMETRY: return "AT_L2_CACHEGEOMETRY";
+#endif
+ }
+ static char name[32];
+ snprintf(name, sizeof(name), "AT_??? (%d)", at);
+ return name;
+}
+
+void ld_show_auxv(ElfW(auxv_t)* auxv) {
+ for (ElfW(auxv_t)* v = auxv; v->a_type != AT_NULL; ++v) {
+ const char* name = auxv_name(v->a_type);
+ long value = v->a_un.a_val;
+ switch (v->a_type) {
+ case AT_SYSINFO_EHDR:
+ case AT_PHDR:
+ case AT_BASE:
+ case AT_ENTRY:
+ case AT_RANDOM:
+ async_safe_format_fd(STDOUT_FILENO, "%-20s %#lx\n", name, value);
+ break;
+ case AT_FLAGS:
+ case AT_HWCAP:
+ case AT_HWCAP2:
+ async_safe_format_fd(STDOUT_FILENO, "%-20s %#lb\n", name, value);
+ break;
+ case AT_EXECFN:
+ case AT_PLATFORM:
+ async_safe_format_fd(STDOUT_FILENO, "%-20s \"%s\"\n", name, reinterpret_cast<char*>(value));
+ break;
+ default:
+ async_safe_format_fd(STDOUT_FILENO, "%-20s %ld\n", name, value);
+ break;
+ }
+ }
+}