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Don't allow pwrite to resize a stream.

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The current implementations could exhibit some behavior differences:

raw_fd_ostream: Whatever the underlying fd does with seek+write. In a normal
file, the write position would be back to the old offset.

raw_svector_ostream: The write position is always the end of the stream, so
after pwrite the write position would be the new end. This matches what OS_X
(all BSD?) do with a pwrite in a O_APPEND fd.

Given that we don't need that feature and don't use O_APPEND a lot in LLVM,
just disallow it.

I am open to suggestions on renaming pwrite to something else, but this fixes
the issue for now.

Thanks to Yaron Keren for reporting it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235303 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola
2015-04-20 13:04:30 +00:00
parent dbef0175c3
commit f30ac8f5ec
3 changed files with 26 additions and 15 deletions
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16
include/llvm/Support/raw_ostream.h
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@@ -317,10 +317,15 @@ private:
/// pwrite operation. This is usefull for code that can mostly stream out data,
/// but needs to patch in a header that needs to know the output size.
class raw_pwrite_stream : public raw_ostream {
virtual void pwrite_impl(const char *Ptr, size_t Size, uint64_t Offset) = 0;
public:
explicit raw_pwrite_stream(bool Unbuffered = false)
: raw_ostream(Unbuffered) {}
virtual void pwrite(const char *Ptr, size_t Size, uint64_t Offset) = 0;
void pwrite(const char *Ptr, size_t Size, uint64_t Offset) {
assert(Size + Offset <= tell() && "We don't support extending the stream");
pwrite_impl(Ptr, Size, Offset);
}
};
//===----------------------------------------------------------------------===//
@@ -348,6 +353,8 @@ class raw_fd_ostream : public raw_pwrite_stream {
/// See raw_ostream::write_impl.
void write_impl(const char *Ptr, size_t Size) override;
void pwrite_impl(const char *Ptr, size_t Size, uint64_t Offset) override;
/// Return the current position within the stream, not counting the bytes
/// currently in the buffer.
uint64_t current_pos() const override { return pos; }
@@ -388,8 +395,6 @@ public:
/// to the offset specified from the beginning of the file.
uint64_t seek(uint64_t off);
void pwrite(const char *Ptr, size_t Size, uint64_t Offset) override;
/// Set the stream to attempt to use atomic writes for individual output
/// routines where possible.
///
@@ -478,6 +483,8 @@ class raw_svector_ostream : public raw_pwrite_stream {
/// See raw_ostream::write_impl.
void write_impl(const char *Ptr, size_t Size) override;
void pwrite_impl(const char *Ptr, size_t Size, uint64_t Offset) override;
/// Return the current position within the stream, not counting the bytes
/// currently in the buffer.
uint64_t current_pos() const override;
@@ -495,7 +502,6 @@ public:
explicit raw_svector_ostream(SmallVectorImpl<char> &O);
~raw_svector_ostream() override;
void pwrite(const char *Ptr, size_t Size, uint64_t Offset) override;
/// This is called when the SmallVector we're appending to is changed outside
/// of the raw_svector_ostream's control. It is only safe to do this if the
@@ -511,6 +517,7 @@ public:
class raw_null_ostream : public raw_pwrite_stream {
/// See raw_ostream::write_impl.
void write_impl(const char *Ptr, size_t size) override;
void pwrite_impl(const char *Ptr, size_t Size, uint64_t Offset) override;
/// Return the current position within the stream, not counting the bytes
/// currently in the buffer.
@@ -519,7 +526,6 @@ class raw_null_ostream : public raw_pwrite_stream {
public:
explicit raw_null_ostream() {}
~raw_null_ostream() override;
void pwrite(const char *Ptr, size_t Size, uint64_t Offset) override;
};
class buffer_ostream : public raw_svector_ostream {