From: Nelson Chu <nelson.chu@sifive.com>
To: binutils@sourceware.org, jrtc27@jrtc27.com
Cc: jimw@sifive.com, kito.cheng@sifive.com, palmerdabbelt@google.com
Subject: [PATCH 1/2] RISC-V: Add description for RISC-V Modifiers to as doc.
Date: Tue, 03 Mar 2020 10:22:00 -0000 [thread overview]
Message-ID: <1583230959-11401-2-git-send-email-nelson.chu@sifive.com> (raw)
In-Reply-To: <1583230959-11401-1-git-send-email-nelson.chu@sifive.com>
gas/
* doc/c-riscv.texi (relocation modifiers): Add documentation.
(RISC-V-Formats): Update the section name from "Instruction Formats"
to "RISC-V Instruction Formats".
---
gas/doc/c-riscv.texi | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 102 insertions(+), 1 deletion(-)
diff --git a/gas/doc/c-riscv.texi b/gas/doc/c-riscv.texi
index 599b5cf..8212a17 100644
--- a/gas/doc/c-riscv.texi
+++ b/gas/doc/c-riscv.texi
@@ -17,6 +17,7 @@
@menu
* RISC-V-Options:: RISC-V Options
* RISC-V-Directives:: RISC-V Directives
+* RISC-V-Modifiers:: RISC-V Assembler Modifiers
* RISC-V-Formats:: RISC-V Instruction Formats
* RISC-V-ATTRIBUTE:: RISC-V Object Attribute
@end menu
@@ -207,8 +208,108 @@ The @var{tag} is either an attribute number, or one of the following:
@end table
+@node RISC-V-Modifiers
+@section RISC-V Assembler Modifiers
+
+RISC-V assembler supports following modifiers for relocatable address
+used in RISC-V instruction operands. However, we also support some
+pseudo instructions to reduce the use of error-prone for these modifiers.
+
+@table @code
+@item %lo(@var{symbol})
+The low 12-bit of absolute address for @var{symbol}.
+
+@item %hi(@var{symbol})
+The high 20-bit of absolute address for @var{symbol}. This is usually
+used with the %lo to represent a 32-bit absolute address.
+
+@smallexample
+ lui a0, %hi(@var{symbol}) // R_RISCV_HI20
+ addi/load/store a0, a0, %lo(@var{symbol}) // R_RISCV_LO12_I/S
+@end smallexample
+
+@item %pcrel_lo(@var{label})
+The low 12-bit of relative address between pc and @var{symbol}.
+The @var{symbol} is related to the high part instrcution which marked
+by @var{label}.
+
+@item %pcrel_hi(@var{symbol})
+The high 20-bit of relative address between pc and @var{symbol}.
+This is usually used with the %pcrel_lo to represent a 4GB pc-relative range.
+
+@smallexample
+@var{label}:
+ auipc a0, %pcrel_hi(@var{symbol}) // R_RISCV_PCREL_HI20
+ addi/load/store a0, a0, %pcrel_lo(@var{label}) // R_RISCV_PCREL_LO12_I/S
+@end smallexample
+
+Or you can use the pseudo lla/lw/sw/... instruction to do this.
+
+@smallexample
+ lla a0, @var{symbol}
+@end smallexample
+
+@item %tprel_add(@var{symbol}
+This is used purely to associate the R_RISCV_TPREL_ADD relocation for
+TLS relaxation.
+
+@item %tprel_lo(@var{symbol})
+The low 12-bit of relative address between tp and @var{symbol}
+
+@item %tprel_hi(@var{symbol})
+The high 20-bit of relative address between tp and @var{symbol}. This is
+usually used with the %tprel_lo and %tprel_add to access the thread local
+variable @var{symbol} in TLS Local Exec.
+
+@smallexample
+ lui a5, %tprel_hi(@var{symbol}) // R_RISCV_TPREL_HI20
+ add a5, a5, tp, %tprel_add(@var{symbol}) // R_RISCV_TPREL_ADD
+ load/store t0, %tprel_lo(@var{symbol})(a5) // R_RISCV_TPREL_LO12_I/S
+@end smallexample
+
+@item %tls_ie_pcrel_hi(@var{symbol})
+The high 20-bit of relative address between pc and GOT entry. It is usually
+used with the %pcrel_lo to access the thread local variable @var{symbol} in
+TLS Inital Exec.
+
+@smallexample
+ la.tls.ie a5, @var{symbol}
+ add a5, a5, tp
+ load/store t0, 0(a5)
+@end smallexample
+
+The pseudo la.tls.ie instruction can be expended to
+
+@smallexample
+@var{label}:
+ auipc a5, %tls_ie_pcrel_hi(@var{symbol}) // R_RISCV_TLS_GOT_HI20
+ ld/lw a5, %pcrel_lo(@var{label})(a5) // R_RISCV_PCREL_LO12_I/S
+@end smallexample
+
+@item %tls_gd_pcrel_hi(@var{symbol})
+The high 20-bit of relative address between pc and GOT entry. It is usually
+used with the %pcrel_lo to access the thread local variable @var{symbol} in
+TLS Global Dynamic.
+
+@smallexample
+ la.tls.gd a0, @var{symbol}
+ call __tls_get_addr@@plt
+ mv a5, a0
+ load/store t0, 0(a5)
+@end smallexample
+
+The pseudo la.tls.gd instruction can be expended to
+
+@smallexample
+@var{label}:
+ auipc a0, %tls_gd_pcrel_hi(@var{symbol}) // R_RISCV_TLS_GD_HI20
+ addi a0, a0, %pcrel_lo(@var{label}) // R_RISCV_PCREL_LO12_I/S
+@end smallexample
+
+@end table
+
@node RISC-V-Formats
-@section Instruction Formats
+@section RISC-V Instruction Formats
@cindex instruction formats, risc-v
@cindex RISC-V instruction formats
--
2.7.4
next prev parent reply other threads:[~2020-03-03 10:22 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-03 10:22 [PATCH 0/2] Add description for the RISC-V relocatable modifiers in " Nelson Chu
2020-03-03 10:22 ` Nelson Chu [this message]
2020-03-03 22:12 ` [PATCH 1/2] RISC-V: Add description for RISC-V Modifiers to " Jim Wilson
2020-03-03 10:22 ` [PATCH 2/2] RISC-V: Support assembler modifier %got_pcrel_hi Nelson Chu
2020-03-03 22:16 ` Jim Wilson
2020-03-04 0:07 ` Fangrui Song
2020-03-04 1:54 ` Nelson Chu
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