arch-arm: Semihosting, specify files root dir

This patch adds an option to "ArmSemihosting" which allows for
specifying an optional search path for host files.
Previously, behaviour was fixed to search in the directory from where
the gem5 binary was run from.

Change-Id: I57b932b38d022f132af78857104633d7bfdd1442
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23903
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/arm/ArmSemihosting.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2018 ARM Limited
+# Copyright (c) 2018, 2019 ARM Limited
 # All rights reserved.
 #
 # The license below extends only to copyright in the software and shall
@@ -52,6 +52,8 @@ class ArmSemihosting(SimObject):
                           "Standard output (stdout for gem5's terminal)")
     stderr = Param.String("stderr",
                           "Standard error (stderr for gem5's terminal)")
+    files_root_dir = Param.String("",
+        "Host root directory for files handled by Semihosting")
 
     mem_reserve = Param.MemorySize("32MB",
         "Amount of memory to reserve at the start of the address map. This "

src/arch/arm/semihosting.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018 ARM Limited
+ * Copyright (c) 2018, 2019 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -138,6 +138,9 @@ ArmSemihosting::ArmSemihosting(const ArmSemihostingParams *p)
       timeBase([p]{ struct tm t = p->time; return mkutctime(&t); }()),
       tickShift(calcTickShift()),
       semiErrno(0),
+      filesRootDir(!p->files_root_dir.empty() &&
+                   p->files_root_dir.back() != '/' ?
+                   p->files_root_dir + '/' : p->files_root_dir),
       stdin(getSTDIO("stdin", p->stdin, "r")),
       stdout(getSTDIO("stdout", p->stdout, "w")),
       stderr(p->stderr == p->stdout ?
@@ -291,6 +294,8 @@ ArmSemihosting::callOpen(ThreadContext *tc, bool aarch64,
         return retError(EINVAL);
 
     std::string fname = readString(tc, name_base, name_size);
+    if (!fname.empty() && fname.front() != '/')
+        fname = filesRootDir + fname;
 
     std::unique_ptr<ArmSemihosting::FileBase> file =
         FileBase::create(*this, fname, mode);

src/arch/arm/semihosting.hh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018 ARM Limited
+ * Copyright (c) 2018, 2019 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -243,6 +243,7 @@ class ArmSemihosting : public SimObject
         FILE *file;
     };
 
+    std::string filesRootDir;
     std::vector<std::unique_ptr<FileBase>> files;
     FILE *stdin;
     FILE *stdout;