Describe assembler relocation functions more precisely

ref.
- RISC-V Unprivileged ISA V20191213, chapter 25
- gcc manual https://sourceware.org/binutils/docs/as/RISC_002dV_002dModifiers.html

Author: hirooih

riscv-asm.md

@@ -217,21 +217,30 @@ Push/pop current options to/from the options stack.
 
 The following table lists assembler relocation expansions:
 
-Assembler Notation          | Description                    | Instruction / Macro
-:----------------------     | :---------------               | :-------------------
-%hi(symbol)                 | Absolute (HI20)                | lui
-%lo(symbol)                 | Absolute (LO12)                | load, store, add
-%pcrel_hi(symbol)           | PC-relative (HI20)             | auipc
-%pcrel_lo(label)            | PC-relative (LO12)             | load, store, add
-%tprel_hi(symbol)           | TLS LE "Local Exec"            | lui
-%tprel_lo(symbol)           | TLS LE "Local Exec"            | load, store, add
-%tprel_add(symbol)          | TLS LE "Local Exec"            | add
-%tls_ie_pcrel_hi(symbol) \* | TLS IE "Initial Exec" (HI20)   | auipc
-%tls_gd_pcrel_hi(symbol) \* | TLS GD "Global Dynamic" (HI20) | auipc
-%got_pcrel_hi(symbol) \*    | GOT PC-relative (HI20)         | auipc
+Assembler Notation          | Description                    | Instruction / Macro  | delta
+:----------------------     | :---------------               | :------------------- | :--------------
+%hi(symbol)                 | Absolute (HI20)                | lui                  | symbol
+%lo(symbol)                 | Absolute (LO12)                | load, store, add     | symbol
+%pcrel_hi(symbol)           | PC-relative (HI20)             | auipc                | symbol - pc
+%pcrel_lo(label)            | PC-relative (LO12)             | load, store, add     | symbol - pc
+%tprel_hi(symbol)           | TLS LE "Local Exec"            | lui                  | symbol - tp
+%tprel_lo(symbol)           | TLS LE "Local Exec"            | load, store, add     | symbol - tp
+%tprel_add(symbol)          | TLS LE "Local Exec"            | add                  |
+%tls_ie_pcrel_hi(symbol) \* | TLS IE "Initial Exec" (HI20)   | auipc                | GOT[symbol] - pc
+%tls_gd_pcrel_hi(symbol) \* | TLS GD "Global Dynamic" (HI20) | auipc                | GOT[symbol] - pc
+%got_pcrel_hi(symbol) \*    | GOT PC-relative (HI20)         | auipc                | GOT[symbol] - pc
 
 \* These reuse %pcrel_lo(label) for their lower half
 
+The linker adds delta[11] to the 20-bit high part, counteracting sign extension
+of the 12-bit low part.
+
+- %*hi(symbol) : delta[31:12] + delta[11]
+- %*lo(symbol) : delta[11:0]
+
+%tprel_add(symbol) is used purely to associate the R_RISCV_TPREL_ADD relocation
+for TLS relaxation.
+
 Labels
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