semihosting: Retrieve stack top from image_info

Remove the write-once field TaskState.stack_base, and use the
same value from struct image_info.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/aarch64/cpu_loop.c

@@ -168,7 +168,6 @@ void target_cpu_copy_regs(CPUArchState *env, target_pt_regs *regs)
         qemu_guest_getrandom_nofail(&env->keys, sizeof(env->keys));
     }
 
-    ts->stack_base = info->start_stack;
     ts->heap_base = info->brk;
     /* This will be filled in on the first SYS_HEAPINFO call.  */
     ts->heap_limit = 0;

linux-user/arm/cpu_loop.c

@@ -504,7 +504,6 @@ void target_cpu_copy_regs(CPUArchState *env, target_pt_regs *regs)
     arm_rebuild_hflags(env);
 #endif
 
-    ts->stack_base = info->start_stack;
     ts->heap_base = info->brk;
     /* This will be filled in on the first SYS_HEAPINFO call.  */
     ts->heap_limit = 0;

linux-user/m68k/cpu_loop.c

@@ -117,7 +117,6 @@ void target_cpu_copy_regs(CPUArchState *env, target_pt_regs *regs)
     env->aregs[7] = regs->usp;
     env->sr = regs->sr;
 
-    ts->stack_base = info->start_stack;
     ts->heap_base = info->brk;
     /* This will be filled in on the first SYS_HEAPINFO call.  */
     ts->heap_limit = 0;

linux-user/qemu.h

@@ -127,7 +127,6 @@ struct TaskState {
     abi_ulong heap_base;
     abi_ulong heap_limit;
 #endif
-    abi_ulong stack_base;
     int used; /* non zero if used */
     struct image_info *info;
     struct linux_binprm *bprm;

linux-user/riscv/cpu_loop.c

@@ -109,7 +109,6 @@ void target_cpu_copy_regs(CPUArchState *env, target_pt_regs *regs)
         exit(EXIT_FAILURE);
     }
 
-    ts->stack_base = info->start_stack;
     ts->heap_base = info->brk;
     /* This will be filled in on the first SYS_HEAPINFO call.  */
     ts->heap_limit = 0;

semihosting/arm-compat-semi.c

@@ -696,7 +696,11 @@ void do_common_semihosting(CPUState *cs)
 
             retvals[0] = ts->heap_base;
             retvals[1] = ts->heap_limit;
-            retvals[2] = ts->stack_base;
+            /*
+             * Note that semihosting is *not* thread aware.
+             * Always return the stack base of the main thread.
+             */
+            retvals[2] = ts->info->start_stack;
             retvals[3] = 0; /* Stack limit.  */
 #else
             retvals[0] = info.heapbase;  /* Heap Base */