forked from OSchip/llvm-project
d3db13af7e
This is an alternative to the continous mode that was implemented in D68351. This mode relies on padding and the ability to mmap a file over the existing mapping which is generally only available on POSIX systems and isn't suitable for other platforms. This change instead introduces the ability to relocate counters at runtime using a level of indirection. On every counter access, we add a bias to the counter address. This bias is stored in a symbol that's provided by the profile runtime and is initially set to zero, meaning no relocation. The runtime can mmap the profile into memory at abitrary location, and set bias to the offset between the original and the new counter location, at which point every subsequent counter access will be to the new location, which allows updating profile directly akin to the continous mode. The advantage of this implementation is that doesn't require any special OS support. The disadvantage is the extra overhead due to additional instructions required for each counter access (overhead both in terms of binary size and performance) plus duplication of counters (i.e. one copy in the binary itself and another copy that's mmapped). Differential Revision: https://reviews.llvm.org/D69740 |
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| .. | ||
| basic.c | ||
| darwin-proof-of-concept.c | ||
| multiple-DSOs.c | ||
| online-merging.c | ||
| pid-substitution.c | ||
| runtime-counter-relocation.c | ||
| set-file-object.c | ||
| set-filename.c | ||