• Jakob Gruber's avatar
    Reland "[code] Move the unwinding info into metadata area" · 82f6863a
    Jakob Gruber authored
    This is a reland of c5379162
    
    The reland fixes Code::clear_padding to correctly clear trailing
    padding.
    
    Original change's description:
    > [code] Move the unwinding info into metadata area
    >
    > Semantically, the unwinding info is a variable-size metadata table
    > with untagged (i.e. no relocation needed) contents, packed inside Code
    > objects. This is just like other metadata tables (safepoint table,
    > handler table, constant pool, code comments); but for historical
    > reasons it's been treated differently so far. Unlike these other
    > tables, the unwinding info was located *after* InstructionEnd, and its
    > size was written to the first 8 bytes after InstructionEnd.
    >
    > This CL makes unwinding info handling more consistent with other
    > metadata tables by writing its offset into a dedicated
    > kUnwindingInfoOffsetOffset header slot, and by moving the actual data
    > inside the [InstructionStart,InstructionEnd[ area. In follow-up CLs,
    > this area will be split into dedicated instruction- and metadata
    > areas.
    >
    > A picture is worth 1000 words, before:
    >
    >  +--------------------------+  <-- raw_instruction_start()
    >  |       instructions       |
    >  |           ...            |
    >  +--------------------------+
    >  |     embedded metadata    |  <-- safepoint_table_offset()
    >  |           ...            |  <-- handler_table_offset()
    >  |                          |  <-- constant_pool_offset()
    >  |                          |  <-- code_comments_offset()
    >  |    padding to the next   |
    >  |  8-byte aligned address  |
    >  +--------------------------+  <-- raw_instruction_end()
    >  |   [unwinding_info_size]  |
    >  |        as uint64_t       |
    >  +--------------------------+  <-- unwinding_info_start()
    >  |       unwinding info     |
    >  |            ...           |
    >  +--------------------------+  <-- unwinding_info_end()
    >
    > After:
    >
    >  +--------------------------+  <-- raw_instruction_start()
    >  |       instructions       |
    >  |           ...            |
    >  +--------------------------+
    >  |     embedded metadata    |  <-- safepoint_table_offset()
    >  |           ...            |  <-- handler_table_offset()
    >  |                          |  <-- constant_pool_offset()
    >  |                          |  <-- code_comments_offset()
    >  |                          |  <-- unwinding_info_offset()
    >  |                          |
    >  +--------------------------+  <-- raw_instruction_end()
    >
    > Bug: v8:11036
    > Change-Id: I649708821acc5365186ca2c9cff2669fc3e91fd3
    > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2484795
    > Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
    > Reviewed-by: Leszek Swirski <leszeks@chromium.org>
    > Commit-Queue: Jakob Gruber <jgruber@chromium.org>
    > Cr-Commit-Position: refs/heads/master@{#70640}
    
    Cq-Include-Trybots: luci.v8.try:v8_linux64_msan_rel_ng
    Tbr: leszeks@chromium.org
    Bug: v8:11036
    Change-Id: I2ea056fe2a53217e0b5ae25661b92f5ddec6fca5
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2485501
    Commit-Queue: Jakob Gruber <jgruber@chromium.org>
    Reviewed-by: 's avatarJakob Gruber <jgruber@chromium.org>
    Reviewed-by: 's avatarDominik Inführ <dinfuehr@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#70645}
    82f6863a
test-code-layout.cc 3.82 KB