From bb4c13143c69c46b1f255437d0338cdf98a3afb8 Mon Sep 17 00:00:00 2001
From: Alex Richardson <alexrichardson@google.com>
Date: Tue, 30 Apr 2024 16:00:03 -0700
Subject: [PATCH 1/2] arch-generic: Fix reading from special
 :semihosting-features file

The implementation of SYS_FLEN was missing, which caused picolibc to
treat this file as not implemented. Additionally, there was a bug in
the SYS_READ call that was comparing the wrong variable against the
passed buffer length. It was comparing the current file position against
the buffer length instead of the number of written bytes.
Finally, pos was unititialized which could result in spurious errors.

Change-Id: I8b487a79df5970a5001d3fef08d5579bb4aa0dd0
---
 src/arch/generic/semihosting.cc | 14 +++++++++++---
 src/arch/generic/semihosting.hh |  5 +++--
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/arch/generic/semihosting.cc b/src/arch/generic/semihosting.cc
index 4da54c4b4b..d8eabedbae 100644
--- a/src/arch/generic/semihosting.cc
+++ b/src/arch/generic/semihosting.cc
@@ -94,7 +94,7 @@ const std::map<uint64_t, const char *> BaseSemihosting::exitCodes{
         {0x20029, "semi:ADP_Stopped_DivisionByZero"},
 };
 
-const std::vector<uint8_t> BaseSemihosting::features{
+const std::array<uint8_t, 5> BaseSemihosting::features{
         0x53, 0x48, 0x46, 0x42, // Magic
         0x3, // EXT_EXIT_EXTENDED, EXT_STDOUT_STDERR
 };
@@ -649,18 +649,26 @@ BaseSemihosting::FileBase::flen()
     return -EINVAL;
 }
 
+static const std::vector<uint8_t> features;
+
 BaseSemihosting::FileFeatures::
 FileFeatures(BaseSemihosting &_parent, const char *_name, const char *_mode) :
     FileBase(_parent, _name, _mode)
 {}
 
+int64_t
+BaseSemihosting::FileFeatures::flen()
+{
+    return features.size();
+}
+
 int64_t
 BaseSemihosting::FileFeatures::read(uint8_t *buffer, uint64_t size)
 {
     int64_t len = 0;
 
-    for (; pos < size && pos < BaseSemihosting::features.size(); pos++)
-        buffer[len++] = BaseSemihosting::features[pos];
+    for (; len < size && pos < features.size(); pos++)
+        buffer[len++] = features[pos];
 
     return len;
 }
diff --git a/src/arch/generic/semihosting.hh b/src/arch/generic/semihosting.hh
index 975cac8b78..8725e25389 100644
--- a/src/arch/generic/semihosting.hh
+++ b/src/arch/generic/semihosting.hh
@@ -323,9 +323,10 @@ class BaseSemihosting : public SimObject
 
         int64_t read(uint8_t *buffer, uint64_t size) override;
         int64_t seek(uint64_t pos) override;
+        int64_t flen() override;
 
       protected:
-        size_t pos;
+        size_t pos = 0;
     };
 
     class File : public FileBase
@@ -540,7 +541,7 @@ class BaseSemihosting : public SimObject
 
     static const std::vector<const char *> fmodes;
     static const std::map<uint64_t, const char *> exitCodes;
-    static const std::vector<uint8_t> features;
+    static const std::array<uint8_t, 5> features;
     static const std::map<const std::string, FILE *> stdioMap;
 
     // used in callTmpNam() to deterministically generate a temp filename

From aa2fade12ed55b413f23fd61dc9820a25588a09b Mon Sep 17 00:00:00 2001
From: Alexander Richardson <mail@alexrichardson.me>
Date: Wed, 1 May 2024 18:00:09 +0100
Subject: [PATCH 2/2] Drop unrelated change

---
 src/arch/generic/semihosting.cc | 2 --
 1 file changed, 2 deletions(-)

diff --git a/src/arch/generic/semihosting.cc b/src/arch/generic/semihosting.cc
index d8eabedbae..7366c831cd 100644
--- a/src/arch/generic/semihosting.cc
+++ b/src/arch/generic/semihosting.cc
@@ -649,8 +649,6 @@ BaseSemihosting::FileBase::flen()
     return -EINVAL;
 }
 
-static const std::vector<uint8_t> features;
-
 BaseSemihosting::FileFeatures::
 FileFeatures(BaseSemihosting &_parent, const char *_name, const char *_mode) :
     FileBase(_parent, _name, _mode)