From 729566b9db41a4425c26ee7fad8c5d1f48355f4c Mon Sep 17 00:00:00 2001
From: Jari Vetoniemi <mailroxas@gmail.com>
Date: Wed, 18 Apr 2018 16:06:36 +0300
Subject: libc: stdio must be wrapped

Bionic libc does stupid stuff and defines standard streams as macros to
reference of an array element. Thus we can't just point standard streams
to their respective correct addresses. (Why does both glibc and bionic
even expose the internal FILE structs??)

So we have to wrap every function that takes FILE* as argument and
mangle it with bionic_file_to_glibc_file. We can't just check addresses
because gnu's libstdc++ copies the FILE*.

I assume same thing happens with the c++ locale support, and we need to
do more complex ctype wrapping.
---
 src/libc-stdio.h   | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/libc-verbose.h | 20 ---------------
 src/libc.c         | 13 +++++-----
 3 files changed, 79 insertions(+), 26 deletions(-)
 create mode 100644 src/libc-stdio.h

diff --git a/src/libc-stdio.h b/src/libc-stdio.h
new file mode 100644
index 0000000..7f09c74
--- /dev/null
+++ b/src/libc-stdio.h
@@ -0,0 +1,72 @@
+#pragma once
+
+struct bionic___sFILE {
+#if defined(__LP64__)
+   char __private[152];
+#else
+   char __private[84];
+#endif
+} __attribute__((aligned(sizeof(void*))));
+
+// Bionic standard stream support pre-M Android
+// Post-M it's saner and they point to stdin/stdout/stderr symbols instead
+const struct bionic___sFILE bionic___sF[3] = {
+   {{ 's', 't', 'd', 'i', 'n' }},
+   {{ 's', 't', 'd', 'o', 'u', 't' }},
+   {{ 's', 't', 'd', 'e', 'r', 'r' }}
+};
+
+static inline FILE*
+bionic_file_to_glibc_file(FILE *f)
+{
+   // Can't compare just memory addresses because GNU libstdc++ copies the FILE struct...
+   // Maybe there could be a cleaner solution, this may in practice break if standard streams
+   // are opened with different flags in C++.
+   if (memcmp(f, "stdin", sizeof("stdin")))
+      return stdin;
+   else if (memcmp(f, "stdout", sizeof("stdout")))
+      return stdout;
+   else if (memcmp(f, "stderr", sizeof("stderr")))
+      return stderr;
+   return f;
+}
+
+FILE*
+bionic_freopen(const char *filename, const char *modes, FILE *stream)
+{
+   return freopen(filename, modes, bionic_file_to_glibc_file(stream));
+}
+
+int
+bionic_fclose(FILE *stream)
+{
+   return fclose(bionic_file_to_glibc_file(stream));
+}
+
+size_t
+bionic_fread(void *ptr, size_t size, size_t nmemb, FILE *stream)
+{
+   char buf[256], fname[256] = {0};
+   stream = bionic_file_to_glibc_file(stream);
+   snprintf(buf, sizeof(buf), "/proc/self/fd/%d", fileno(stream));
+   readlink(buf, fname, sizeof(fname));
+   verbose("%s (%d)\n%p, %zu, %zu, %p", fname, fileno(stream), ptr, size, nmemb, (void*)stream);
+   return fread(ptr, size, nmemb, stream);
+}
+
+size_t
+bionic_fwrite(void *ptr, size_t size, size_t nmemb, FILE *stream)
+{
+   char buf[256], fname[256] = {0};
+   stream = bionic_file_to_glibc_file(stream);
+   snprintf(buf, sizeof(buf), "/proc/self/fd/%d", fileno(stream));
+   readlink(buf, fname, sizeof(fname));
+   verbose("%s (%d)\n%p, %zu, %zu, %p", fname, fileno(stream), ptr, size, nmemb, (void*)stream);
+   return fwrite(ptr, size, nmemb, stream);
+}
+
+int
+bionic_fflush(FILE *stream)
+{
+   return fflush(bionic_file_to_glibc_file(stream));
+}
diff --git a/src/libc-verbose.h b/src/libc-verbose.h
index 190f0b1..2d46f17 100644
--- a/src/libc-verbose.h
+++ b/src/libc-verbose.h
@@ -144,26 +144,6 @@ bionic_unlink(const char *path)
    return unlink(path);
 }
 
-size_t
-bionic_fread(void *ptr, size_t size, size_t nmemb, FILE *stream)
-{
-   char buf[256], fname[256] = {0};
-   snprintf(buf, sizeof(buf), "/proc/self/fd/%d", fileno(stream));
-   readlink(buf, fname, sizeof(fname));
-   verbose("%s (%d)\n%p, %zu, %zu, %p", fname, fileno(stream), ptr, size, nmemb, (void*)stream);
-   return fread(ptr, size, nmemb, stream);
-}
-
-size_t
-bionic_fwrite(void *ptr, size_t size, size_t nmemb, FILE *stream)
-{
-   char buf[256], fname[256] = {0};
-   snprintf(buf, sizeof(buf), "/proc/self/fd/%d", fileno(stream));
-   readlink(buf, fname, sizeof(fname));
-   verbose("%s (%d)\n%p, %zu, %zu, %p", fname, fileno(stream), ptr, size, nmemb, (void*)stream);
-   return fwrite(ptr, size, nmemb, stream);
-}
-
 char*
 bionic_getenv(const char *name)
 {
diff --git a/src/libc.c b/src/libc.c
index 66b0d8d..447220e 100644
--- a/src/libc.c
+++ b/src/libc.c
@@ -14,10 +14,6 @@
 #include <netdb.h> // h_errno
 #include  "wrapper/verbose.h"
 
-#ifdef VERBOSE_FUNCTIONS
-#  include "libc-verbose.h"
-#endif
-
 struct bionic_dirent {
    uint64_t d_ino;
    int64_t d_off;
@@ -74,9 +70,10 @@ tkill(int tid, int sig)
 // Stuff needed for runtime compatibility, but not neccessary for linking
 // Also stuff that exists in glibc, but needs to be wrapped for runtime compatibility
 
+#include "libc-stdio.h"
+
 const char *bionic__ctype_, *bionic__tolower_tab_, *bionic__toupper_tab_;
-char bionic___sF[0x54] = {0};
-unsigned int bionic___page_size = PAGE_SIZE;
+const unsigned int bionic___page_size = PAGE_SIZE;
 
 __attribute_const__
 int*
@@ -378,3 +375,7 @@ bionic___futex_wake(volatile void* ftx, int count)
    return syscall(SYS_futex, ftx, FUTEX_WAKE, count, NULL, 0);
 }
 #endif
+
+#ifdef VERBOSE_FUNCTIONS
+#  include "libc-verbose.h"
+#endif
-- 
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