Re: [Qemu-devel] [PATCH] linux-user: identify running binary in /proc/self/exe

[Riku Voipio <riku.voipio@iki.fi>]

Some applications like to test /proc/self/exe to find
out who they are. Fake the result of readlink() for
them. Use realpath() to return full path to binary
(which the links /proc/self/exe are)

updated version - fix ret/errno in the /proc/self/exe case.

Signed-off-by: Riku Voipio <riku.voipio@iki.fi>
---
 linux-user/main.c    |    3 +++
 linux-user/qemu.h    |    1 +
 linux-user/syscall.c |   15 ++++++++++++---
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/linux-user/main.c b/linux-user/main.c
index cb10173..3418ca6 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -37,6 +37,8 @@
 
 #define DEBUG_LOGFILE "/tmp/qemu.log"
 
+char *exec_path;
+
 static const char *interp_prefix = CONFIG_QEMU_PREFIX;
 const char *qemu_uname_release = CONFIG_UNAME_RELEASE;
 
@@ -2354,6 +2356,7 @@ int main(int argc, char **argv, char **envp)
     if (optind >= argc)
         usage();
     filename = argv[optind];
+    exec_path = argv[optind];
 
     /* Zero out regs */
     memset(regs, 0, sizeof(struct target_pt_regs));
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 9fddd05..4137567 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -120,6 +120,7 @@ typedef struct TaskState {
     uint8_t stack[0];
 } __attribute__((aligned(16))) TaskState;
 
+extern char *exec_path;
 void init_task_state(TaskState *ts);
 extern const char *qemu_uname_release;
 
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 690df14..2903bf3 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -4877,13 +4877,22 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
 #endif
     case TARGET_NR_readlink:
         {
-            void *p2;
+            void *p2, *temp;
             p = lock_user_string(arg1);
             p2 = lock_user(VERIFY_WRITE, arg2, arg3, 0);
             if (!p || !p2)
                 ret = -TARGET_EFAULT;
-            else
-                ret = get_errno(readlink(path(p), p2, arg3));
+            else {
+                if (strncmp((const char *)p, "/proc/self/exe", 14) == 0) {
+                    char real[PATH_MAX];
+                    temp = realpath(exec_path,real);
+                    ret = (temp==NULL) ? get_errno(-1) : strlen(real) ;
+                    snprintf((char *)p2, arg3, "%s", real);
+                    }
+                else
+                    ret = get_errno(readlink(path(p), p2, arg3));
+                break;
+            }
             unlock_user(p2, arg2, ret);
             unlock_user(p, arg1, 0);
         }
-- 
1.5.6.5