i#3544 RV64: Rebase the dcontext pointer. #7235
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The dcontext_t struct is larger than the biggest valid displacement of the load and store instructions. By rebasing the pointer by 0x800, we van access the entire struct, because the dispacement can be in the renge of -0x800 to 0x7ff.
Also worked around build failure on windows
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I know that these patches are quite "hacky". However, I could not find a better way to work around some issues. |
| * substracting 0x800 from the offset in the struct. | ||
| */ | ||
| #ifdef RISCV64 | ||
| # define CONTEXT_REBASE_OFFT 0x800 |
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Suggest a better name such as CONTEXT_HEAD_OFFSET.
I wonder whether a negative offset will be more descriptive than using subtraction everywhere, which gives a hint about the memory layout (REG_DCTX points to the middle of dcontext_t, yielding a negative offset).
| * and it does not run windows, we can work around that with conditional compilation. | ||
| */ | ||
| #if (CONTEXT_REBASE_OFFT != 0) | ||
| (*entry)(((void *)dcontext) + CONTEXT_REBASE_OFFT); |
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Conversion between REG_DCTX and the real head of dcontext_t occurs several times. Suggest wrap these into macros. (CONTEXT_PTR_TO_HEAD() and CONTEXT_HEAD_TO_PTR).
| #if (CONTEXT_REBASE_OFFT != 0) | ||
| set_thread_private_dcontext(NULL); | ||
| #endif |
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Existing code compares thread private dcontext with NULL for validation check, thus this is required or they will get NULL - CONTEXT_REBASE_OFFSET and wrongly assumes thread private dcontext is ready.
Do I understand it correcly? If so, some comments to explain this call seem helpful.
The dcontext_t struct is larger than the biggest valid displacement of the load and store instructions.
By rebasing the pointer by 0x800, we can access the entire struct, because the displacement can be in the range of -0x800 to 0x7ff.