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Update doc
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108
README.md
108
README.md
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@ -1146,11 +1146,11 @@ We look up Code Address 0x50208086 in our NuttX Disassembly...
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```text
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000000005020807a <modifyreg32>:
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up_irq_save():
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/Users/Luppy/ox64/nuttx/include/arch/irq.h:689
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nuttx/include/arch/irq.h:689
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5020807a: 4789 li a5,2
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5020807c: 1007b7f3 csrrc a5,sstatus,a5
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modifyreg32():
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/Users/Luppy/ox64/nuttx/arch/risc-v/src/common/riscv_modifyreg32.c:52
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nuttx/arch/risc-v/src/common/riscv_modifyreg32.c:52
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{
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irqstate_t flags;
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uint32_t regval;
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@ -1158,10 +1158,10 @@ modifyreg32():
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flags = spin_lock_irqsave(NULL);
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regval = getreg32(addr);
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50208080: 4118 lw a4,0(a0)
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/Users/Luppy/ox64/nuttx/arch/risc-v/src/common/riscv_modifyreg32.c:53
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nuttx/arch/risc-v/src/common/riscv_modifyreg32.c:53
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regval &= ~clearbits;
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50208082: fff5c593 not a1,a1
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/Users/Luppy/ox64/nuttx/arch/risc-v/src/common/riscv_modifyreg32.c:52
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nuttx/arch/risc-v/src/common/riscv_modifyreg32.c:52
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regval = getreg32(addr);
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50208086: 2701 sext.w a4,a4
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```
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@ -1354,7 +1354,7 @@ MTVAL: 00000000e0002100
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Code Address is 0x50207e6a, from our PLIC Code...
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```text
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/Users/Luppy/ox64/nuttx/arch/risc-v/src/chip/jh7110_irq.c:62
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nuttx/arch/risc-v/src/chip/jh7110_irq.c:62
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putreg32(0x0, JH7110_PLIC_ENABLE1);
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50207e64: 700017b7 lui a5,0x70001
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50207e68: 0786 slli a5,a5,0x1
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@ -2542,6 +2542,104 @@ Right after that, [__nx_bringup__](https://github.com/apache/nuttx/blob/master/s
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- [__ELF Loader: g_elfbinfmt__](https://github.com/lupyuen2/wip-pinephone-nuttx/blob/ox64b/binfmt/elf.c#L84-L94) to load the ELF File (explained above)
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# Simple NuttX App for Ox64 BL808
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_What's inside the simplest app for NuttX?_
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From [hello_main.c](https://github.com/lupyuen2/wip-pinephone-nuttx-apps/blob/ox64b/examples/hello/hello_main.c#L36-L40)
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```c
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int main(int argc, FAR char *argv[]) {
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printf("Hello, World!!\n");
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return 0;
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}
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```
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Here's the RISC-V Disassembly: [hello.S](https://github.com/lupyuen2/wip-pinephone-nuttx/releases/download/ox64a-1/hello.S)
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```text
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000000000000003e <main>:
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main():
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apps/examples/hello/hello_main.c:37
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/****************************************************************************
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* hello_main
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****************************************************************************/
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int main(int argc, FAR char *argv[])
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{
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3e: 1141 addi sp,sp,-16
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apps/examples/hello/hello_main.c:38
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printf("Hello, World!!\n");
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40: 00000517 auipc a0,0x0 40: R_RISCV_PCREL_HI20 .LC0
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40: R_RISCV_RELAX *ABS*
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44: 00050513 mv a0,a0 44: R_RISCV_PCREL_LO12_I .L0
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44: R_RISCV_RELAX *ABS*
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0000000000000048 <.LVL1>:
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apps/examples/hello/hello_main.c:37
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{
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48: e406 sd ra,8(sp)
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apps/examples/hello/hello_main.c:38
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printf("Hello, World!!\n");
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4a: 00000097 auipc ra,0x0 4a: R_RISCV_CALL puts
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4a: R_RISCV_RELAX *ABS*
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4e: 000080e7 jalr ra # 4a <.LVL1+0x2>
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0000000000000052 <.LVL2>:
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apps/examples/hello/hello_main.c:40
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return 0;
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}
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52: 60a2 ld ra,8(sp)
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54: 4501 li a0,0
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56: 0141 addi sp,sp,16
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58: 8082 ret
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```
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We see that [main](https://github.com/lupyuen2/wip-pinephone-nuttx-apps/blob/ox64b/examples/hello/hello_main.c#L36-L40) calls...
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- [puts](https://github.com/lupyuen2/wip-pinephone-nuttx/blob/ox64b/libs/libc/stdio/lib_puts.c#L34-L96), which calls...
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- [lib_fwrite_unlocked](https://github.com/lupyuen2/wip-pinephone-nuttx/blob/ox64b/libs/libc/stdio/lib_libfwrite.c#L45-L200), which calls...
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- [stream->fs_iofunc.write](https://github.com/lupyuen2/wip-pinephone-nuttx/blob/ox64b/libs/libc/stdio/lib_libfwrite.c#L145) OR...
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[write](https://github.com/lupyuen2/wip-pinephone-nuttx/blob/ox64b/libs/libc/stdio/lib_libfwrite.c#L149) (See below)
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TODO: Which one?
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TODO: _start prepares sig_trampoline and calls main
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_This code doesn't look right..._
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```text
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apps/examples/hello/hello_main.c:38
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printf("Hello, World!!\n");
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4a: 00000097 auipc ra,0x0
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4e: 000080e7 jalr ra
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```
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That's because this is __Relocatable Code__. The auipc offset will be fixed up by the NuttX ELF Loader when it loads this code into User Memory.
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The Relocation Info shows that 0x0 will be replaced by the address of `puts`...
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```text
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4a: 00000097 auipc ra,0x0
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4a: R_RISCV_CALL puts
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4e: 000080e7 jalr ra
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```
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_Why `puts` instead of `printf`?_
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The GCC Compiler has cleverly optimised away `printf` to become `puts`.
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If we do this...
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```c
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printf("Hello, World %s!!\n", "Luppy");
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```
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Then `printf` will appear in our disassembly.
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# NuttX App calls NuttX Kernel
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TODO
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