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Improve grammar and wording in 'Mapping Symbol' section #441

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Improve grammar and wording in 'Mapping Symbol' section #441

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33 changes: 17 additions & 16 deletions riscv-elf.adoc
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Expand Up @@ -1369,29 +1369,30 @@ A number of symbols, named mapping symbols, describe the boundaries.
The mapping symbol should set the type to `STT_NOTYPE`, binding to `STB_LOCAL`,
and the size of symbol to zero.

The mapping symbol for data(`$d`) indicates the start of a sequence of data bytes.
The mapping symbol for data(`$d`) indicates the start of a sequence of data
bytes.

The mapping symbol for instruction(`$x`) indicates the start of a sequence of
instructions.
and it has an optional ISA string, which means the following code regions are
using ISA is different than the ISA recorded in the arch attribute;
the ISA information will used until the next instruction mapping symbol;
an instruction mapping symbol without ISA string means using ISA configuration
from ELF attribute.

Format and rule of the optional ISA string are same as `Tag_RISCV_arch`, must
having explicit version, more detailed rule please refer to <<Attributes>>.
instructions. It has an optional ISA string that indicates the following code
regions are using ISA which is different from the ISA recorded in the arch
attribute. The optional ISA information, when present, will be used until the
next instruction mapping symbol. An instruction mapping symbol without ISA
string means using ISA configuration from ELF attribute. The format and rules
of the optional ISA string are same as `Tag_RISCV_arch` and must have explicit
version. For more detailed rules, please refer to <<Attributes>>.

The mapping symbol can be followed by an optional uniquifier, which is prefixed
with a dot (`.`).

NOTE: The use case for mapping symbol for instruction(`$x`) with ISA information
is used with ifunc, e.g. libraries are built with `rv64gc`, but few functions
like memcpy provides two versions, one built with `rv64gc`, and one built with
`rv64gcv`, and select by ifunc mechanism at run-time; however, the arch
attribute is recording for minimal execution environment requirements, so the
ISA information from arch attribute is not enough for the disassembler to
disassemble the `rv64gcv` version correctly.
is used with `IFUNC`. Consider a scenario where C library is built with `rv64gc`
but few functions like memcpy may provide two versions, one built with `rv64gc`
and another built with `rv64gcv`, and the `IFUNC` mechanism selects one version
of those at run-time. However, the arch attribute is recorded for the minimal
execution environment requirements, so the ISA information from arch attribute
is not enough for the disassembler to disassemble the `rv64gcv` version
correctly. Specifying ISA string appropriately with the two memcpy instruction
mapping symbols helps the disassembler to disassemble instructions correctly.

== Linker Relaxation

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